1. people to retain their anonymity.
2. trolls to evade bans on websites.
3. idiots to access websites they shouldn't be accessing when they should be working.
Proxies are usually marketed towards the latter.
2. Troll: About time they banned me. Time to use a proxy...
3. Idiot: lyk omgz did u no der r deez thingz calld proxiz && u can uze dem 2 get on myspace wen ur at skool????/
person 2: try this proxy website it unblocks everything
person 1: everything??!!
person 2: EVERYTHING!!!!!
person 1: cheers m8