Personally I like to keep many files open so that I have undo buffers for them in case I change my mind. This is a subjective thing and I know there are other

Personally I like to keep many files open so that I have undo buffers for them in case I change my mind. This is a subjective thing and I know there are other ways to solve the same issue (keeping versioned files ala Dropbox, etc), but easy undo of recent-but-not-too-recent changes is the #1 reason I tend to keep tons of files open when editing projects.