^^^ I think you figured it out. The "rules" are really just guidelines. It is understanding why they are rules is what is important so that you can consciously decide how to dress. Many of the rules are based on "tradition" or culture while other (more important IMHO) rules revolve around physique and silhouette.
I was just reading an article or post about pocket squares. It seems that the consensus on this forum, and in most parts, is that a pocket square should compliment (not match) a color in your shirt, tie or jacket. Well this article stated that (the British I believe) look down on this practice and that a PS should be thrown in your pocket randomly; as in reaching into a drawer blindfolded and using whatever you grab, as in "I put no thought into this." So taking all of this into account, if we are in a non-British (if that's who was cited) environment and decide to wear a random "non-complimentary" pocket square anyway...well at least we knew the "rules" and broke them. A lot of it comes down to what your goals and mood are and whether you want to blend/conform or draw attention to yourself. Generally I think most here strive for an element of sprezzatura
(a word that even after more than a year here I can't spell without Googling it)
Another example would be a 5' man wearing a 6/2 double breasted suit with a bold window pane. Both of these choices "widen" the body (as opposed to elongating it) and while it can be done, these are not the best choices. A better choice (by conventional wisdom anyway) would be a single breasted suit with pinstripes. These are the rules that are more "set in stone" if one is overly short/tall or thin/wide.
My take on cuffs/no cuffs and pleats/no pleats is this. Pleats make a wide person wider and flat fronts tend to be more slimming. Cuffs tend to "even out" pleats, especially as most pleated pants are also tapered. Flat-fronts are generally not as tapered (looking anyway) and don't need to be "evened out" and therefore do not need cuffs. Cuffs break the vertical line which is not good for shorter men. The "purpose" of cuffs (outside of stylistic preferences) is to weigh the pant leg down so that it drapes properly and doesn't flail around while walking. I'm pretty slim but have a very arched back and my gut sticks out. Flat-fronts look kind of odd to me on my body so I avoid them. I'm on the shorter side so avoid cuffs except when in a suit (cuffs seem more formal to me and a suit without cuffed pants seems too casual).
But again, I think you hit the nail on the head...everyone has their opinion and it's not that any particular one is "right" or "wrong" but what works for you in your particular situation and mood.