It just depends on what type of patch you are talking about?
There are some patches that bypass copy protections, and some that convert a game from PAL to NTSC.... etc.....
NOTE: If you use Clone CD with a 100% compatible writer, you do not need to patch CD based games... Clone CD will copy the protection and all.......
Also..... 99.99% of DVD based games have NO protection so you do not have to patch those either.....