Saving during combat isn't really useful for much more than re-planning your moves, which of course is a huge thing in and of itself. But it won't, for example, reset your hit chances or anything.
As of 188.8.131.522 it does apparently
From the release notes:
Fixed random seed not being reset when loading a savegame. Happy save scumming!
I don't mind either way. I don't do it much unless the combat is really long. If someone wants to do it though it is no skin off my nose. There are more efficient (cheesier) ways to cheat if you feel like it anyway.
At the moment with bugs that make the game freeze and your characters lose all their skills it is pretty much essential.