If you're reading this, you probably know how movement factors work. You move the unit from hex to hex (or square to square, or area to area, or whatever to whatever), expending a certain number of movement points for each hex entered. I'm going to assume that if you know that, you also know that a unit cannot exceed its movement factor, unless the rules make some kind of exception (for example, that the unit can always move one hex during a Movement Phase, even if it doesn't actually have sufficient MPs to enter that one hex).
So, serious question - if you have two units, and each have 5 MPs, and one of those units uses 3 MP, can it "lend" its leftover 2 MP to the other, allowing it to expend 7 MP? No? Well, what about if that first unit uses 3 MP, can it save its other 2 MP and apply it to the next turn? Still no?
Some games have rules that will explicitly forbid that kind of thing: Movement points may not be accumulated from turn to turn or phase to phase, nor may they be loaned or given from one unit or stack to another. But there's just as many that don't. That doesn't mean of course that the players can split off and save up MPs to their heart's content, and I've yet to meet any gamer who thinks that's the case. Similarly, some rulesets state that movement is from hex to contiguous hex, without skipping any hexes, while others just state hex to hex. Outside of a game of Battles on the Ice with a ten-year-old who, Turtledove-like, had gifted the mounted knights of the Livonian Order with teleporting equipment, I don't know of anyone who would read hex to hex and say, "Whoa, it doesn't say no skipping, and doesn't specify that those hexes must be contiguous - obviously I can bamf my guys all over the map."
When I write rules, I don't usually take the time to specify that you can't skip hexes when moving, or to forbid the splitting-off and saving-up of movement factors. One could chalk it up to a sort of natural laziness on my part - you do enough of these things, you get tired of typing out the same verbiage again and again, and want to just get to the good stuff - but really, I think it comes from a respect for my audience. These things are so common sense - so foundational - that I honestly think anyone smart enough to play a wargame is smart enough to understand these concepts without me spelling out everything that you can't or shouldn't do.
This is not an uncontroversial opinion among my fellow rules-writers, many of whom approach it like writing instructions for operation of the Holy Hand Grenade: First, shalt thou take out the holy pin. Then, shalt thou count to three. No more, no less. Three shall be the number thou shalt count, and the number of the counting shall be three. Four shalt thou not count, neither count thou two, excepting that thou then proceed to three. Five is right out. Once the number three, being the third number, be reached, then lobbest thou thy Holy Hand Grenade of Antioch.
And while that's the gag in this case, it's not really that far off from the way many wargame rulebooks have been traditionally written. Though I'm sure there will be wise-guys going on about how those instructions are incomplete, because it doesn't specify that you should count by whole numbers and not fractions, beginning with one - the rules don't reference the number one anywhere! - and then somebody else will break in that they don't know what "beginning with one" means: is the first number you count one, or is the first number two, since you're starting at one?
I'm only kidding here, and I want to be clear that none of this is in reference to legitimate rules queries that arise from ambiguous wording. I'm only saying that one should be able to say "count to three" without forbidding every sort of aberrance someone wants to try to tease out of that phrase. The guys who are going to well, technically the system are going to well, technically it anyway. I am reminded for example of the story of the fellow who bought two copies of Combat Commander so that he could excise the bad cards from the deck, arguing that the rules only stated that each nationality has a specific deck of 72 cards, and they did not expressly forbid splicing two such decks together. I just don't think it's worth my time, writing the rules, and your time, reading the rules, for me to try to deprive bad actors of opportunities: it doesn't stop them, and in fact only encourages them to get more creative and vicious.
My two assumptions about wargamers are as follows: first, that they are going to approach the game and its rules in good faith, and second, that they're at least as smart as I am - which is a pretty low hurdle to clear! Together, those two things allow me to prize simplicity over elaboration, and readability over exhaustiveness.
But it's not just the wiggly dissemblers that inform rules writing decisions, and indeed, most folks who go in for a more exhaustive style of rules writing do it with newbies in mind. Every game might be someone's first game, after all. One can't assume that a complete newbie will be able to speak wargame-ese with any fluency; a ruleset that leaves the "common sense" things unstated throws up invisible, and frustrating, walls for them to crash into. The hobby needs new recruits, and we must be as welcoming as possible. Or so the argument goes.
Thou shall not place thy chits within the vessel that containeth the sacred beverage.
I'm not entirely convinced. Not about the need to be welcoming - that, I agree with one hundred percent! But I disagree - with a caveat - with the idea that being welcoming is the same as explaining that when using a coffee cup for a chit-pull game, that one should ensure there is no coffee in said cup. If you explain every little thing, you end up with blocks and blocks of eye-blearing text, and pages and pages of rules. Page count is a barrier to entry; long, seemingly endless paragraphs are another. There's a reason why so few people read In Search of Lost Time, and it ain't because our boy Marcel skimped on the details. Wargames' reputation for inscrutability and difficulty has more to do with rulebooks that take twenty pages to communicate what could be said in eight. The need to be ridiculously exhaustive is one of the reasons for this.
But I did promise that there was a caveat to all this, and it's this: one can of course be too concise, and what's "common sense" for one person might not be for someone else. (The sheer number of everyday things that Mary has had to patiently, and not-so-patiently, explain to me is mindboggling.) Everyone learns and processes information differently, and the question of where one draws the line doesn't always have an obvious answer. I have had some experienced grognards struggle somewhat with the terse wording of my rules, for example, and it's one reason why we're putting more work into Player Aids and other supporting documentation. And, conversely, some newer gamers have found my rulesets much easier to understand, precisely because it keeps things simple and clean, yet expressive.
Like every other creative endeavor, writing rules is much more of an art than a science, and like everything created by humans, it's prone to imperfection. One simply does the best that one can, and tries to learn from, and improve upon, past mistakes, with an eye toward clarity and accessibility.