Differences Between Torrented and Purchases

Hey guys I was wondering if there is a difference between installing San Andreas from a CD or getting it from a Torrent site? Ik for a fact if you some games that have Multiplayer mods for them that they sometimes don't work... I am downloading a torrent version of SA right now to compare the two but I was wondering what you guys think?

They are both the same, been playing with " fake " version on SA for like 2-3 years now, no problems in SP or MP.