I generally don't like seeing commented-out code in source control because you don't have any idea why it was commented out. Is it something that you added to debug while in the middle of a bug fix, and thus now useless? Is it a half-done refactoring that you ran out of time for or ended up not needing? Is it an attempt at a speedup or new feature that didn't work out? Did it have some tricky bug and get replaced by code that fixed it?
I can't think of any reason to do it that isn't a half-assed attempt at something a good source control system does much better. If you have lightweight branches, blame, and logs you can search and check by date, along with good changeset comments, then you already have everything your commented-out code can do, and all in the same place and system, instead of spread out into several different systems.