Because rebase, and rebase -i especially, gives you the ability to break your patches into discrete this-one-one-goddamn-thing patches (which is awkward in a "oh, you committed it? Then you committed it forever" SCM like Perforce or SVN), you should do so. It makes it a lot easier to review than the "so this does X, but also fixes some syntax errors and adds logging" style. And that means you should make the patch comment reflect what it is doing. Some errors here are inevitable but it's something to which I aspire.
Edit: to be a little clearer; your traditional SCM has a write-once-never-change model for the trunk of development. This has a problem in a peer review situation, and the problem is this: I may go forth with the best of intentions to decompose things into discrete patches. But when you get down to brass tacks, changes to the system tend to happen in any given order--you might discover a latent bug when testing your feature that has nothing to do with your feature. Now you have two choices: you can wait and commit nothing until everything is great, which means you're not integrating with the mainline, which means that integrating will be incredibly painful, which leads to locks; or you commit as it comes in the moment, which is much better for integration and much easier to back out partial changes and generally get all of the non-backup elements of an SCM, but which is the very devil to peer review. With rebase -i, it is quite easy to commit in the second style in the moment and then clean them up for peer review later; that is the ability to revise history means you can make decisions immediately without worrying that they will be cast in stone forever and ever anon.
I wasn't always this much of a hardliner on the subject, but my current job uses Perforce as the main SCM and I have realized that I disagree with almost every decision Perforce makes across the board. I still use it, because any SCM is way better than no SCM and I don't want to explain git to everyone else, but my actual development occurs with git-p4.
