I tend to have different techniques for different situations. For instance, when wrapping an existing chunk of code in an "if" statement or "while" loop, I'll check in the initial change without re-indenting the existing code. Maybe I'll half-indent the new parts or maybe not indent them at all. Either way, that makes the diff readable. Then I'll do a re-indent and check that in, but to me that's ok since it's just a "whitespace" checkin.