I only recently came across the fixltx2e package. Given that it patches aspects of LaTeX, my spidey-sense begins to tingle out of a concern for possible package conflicts.
Are there known conflicts? Is it better to load fixltx2e early, or, like hyperref, as late as possible? (Yes, I am worrying about a problem I don't as yet have. But, the concern won't be fresh in my mind six months from now if some conflict produces a hard to figure out bug.)
I'd originally thought that there was little documentation, as none is linked on the CTAN Catalogue page that I used as the package link. In light of the answer, I thought to run
texdoc fixltx2e1 in the terminal. It turns out there is an extensive amount of documentation available, just not where I am used to looking for a new package.