It also fixes some problems:
1. The original release doesn't compress save files. Rev A does.
2. The original release had a problem opening some Windows-originated save files. It would open them, but then could not save the game later. This was partially fixed in Rev A.
3. The original release has issues with some mods. Rev A solved most of them, but is still not perfect.
Problems 1 and 2 can be solved without the patch, by using my FileValet utility. See my sig for a link. Problem 3 doesn't exist if you don't play mods, but can be hard to work round if you do.
n the down side, I know some people don't run the patch because it appears to have slowed Civ3 down for them.