Why do pc games need the cd to play?

Question

I am just wondering why the pc needs the cd when it uses about 4-7gigs your pc, so whats the need for the cd?

Answer 1

I would hazard a guess here and say it's for anti-p****y reasons.  

Answer 2

The cd is used to prove that you have the right to play this game. If you didn't have the disc then the publishers won't make any money since your just going to borrow the game from one of your friends and you can play it without having to pay.

Answer 3

so you cant be playing it on multiple computers at the same time

so you cant rip off the game maker

Answer 4

you could just get a CD crack for the game and you wont need a cd