One thing that you won't find in most of my work is optional rules, variants, and "advanced" versions, for the simple reason that I don't like them - not as a player and not as a designer.
As a publisher, Mary and I are more agnostic: while we don't really have much use for these kinds of "extra" rules, there are designers who do. Ours is a fundamentally auteurist approach, so if the designer's vision involves having optional rules and variants, we will support and present that vision to the gaming public. For example, Sean Chick conceived his Horse & Musket as a sort of sandbox that players could customize to suit their tastes, pulling from a list of literally dozens of optional rules. Some of these variants aren't necessarily meant to function together: you couldn't play a match using all the fixins, but you could take this one and that one in order to reflect or explore your thinking regarding the period and/or your preferred level of tactical detail. That's absolutely not how I would approach designing a game - the very thought of it makes me twitchy - but that's okay. Sean and I are different people with different approaches, and as I said, our job is to support his vision, not superimpose our own.
When I get Horse & Musket on the table, I stick to the "core" rules, and this is generally my approach with any game that I play. Partially this is a function of bandwidth. I have a hard enough time remembering all the "real" rules, let alone any extras. And partially this is because I tend to value coarse-grain simulations over highly detailed ones, speed over bogging down, simplicity and elegance over fiddliness.
And those same reasons that deter me from optional rules as a player generally hold for me as a designer as well. However, there is the additional wrinkle that as a designer, I feel that if a rule or mechanism had something to contribute to the game, it would already be in the game, as a "normal" rule. I am reminded of that famous bit from Strunk and White - no, not the bit about always forming the possessive of a singular noun with an apostrophe and an "s", even if the noun ends in an "s", Charles's not Charles', and YES, THIS IS THE HILL I AM PREPARED TO DIE ON - but this bit:
Vigorous writing is concise. A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts. This requires not that the writer make all sentences short or avoid all detail and treat subjects only in outline, but that every word tell.
Every rule likewise has to "tell". If it doesn't, then I don't need it, and neither does the player. If it does "tell" - if I do need it - I'm not about to cordon it off in the "advanced" section, where some players (myself included) will never see it.