Like the last two posters, I know few spreads and I rarely use the ones I do know. The spreads I enjoy using are those that are like questions unto themselves (spreads, for example, that ask 'who am I?' or 'what do I need to know')...and often those turn out well, because I am not trying to fit a question to a pre-made spread.
I find, however, that when I have an actual question, the best way to go about laying out the cards is with my intuition. When I begin with no spread, I often find myself creating a spread as I lay them out (like...as I lay them out, I will think 'these three are for the issue at hand...this one I am placing underneath because it is the underlying issue...this I am placing above becuase it is overshadowing the issue at hand...and these two are the overview"). I find this to be highly effective. When using spreads, I struggle with fitting each card into the mold that the spread designated for that placement....and then fitting that mold to the question. Not having to worry about so many rules is better for me.
My opinion on this, pretty much is that you *should* go with your inutition when laying out cards, just the same as you do with reading. Interpretation is only part of the puzzle. Even if you prefer to use spreads...there is a reason you are getting that urge to put a second card in that position, or add an extra overview card...or whatever other urge you are getting, right? Just go with it. Personally, if I got that urge but stuck to the spread, I would be concerned, the whole time I did the reading, that I was interpeting things wrong because I wasn't listening to my intuition in the layout. But I guess it could go both ways - if I did listen to my intuition, rather than follow the spread, I might be concerned that I screwed up the spread by not laying them out according to plan. Perhaps this is why I choose not to use spreads haha.