I find this to be a questionable practice. When coding I like the idea of "trim whitespace from _my changes_ on save", but doing it globally within a file creates a lot of diffs and makes for convoluted commits. Having a +/- 75 lines when you fix a typo in a comment is annoying when doing a code review.

If everybody on the team uses SublimeText (or an equivalent vim extension) I think this is a good idea, but when you have some folks using TextMate or other editors that are notorious for leaving extra whitespace, I find it better just to live with it.

Yep, so if you put this on, make sure you override it back in the Markdown-specific settings.