That is good question, actually. I never asked myself the why of needing them. I have always imagined that it would be someone to trust, someone to relate to, who also understands me. Also, having rich intellectual, thought provoking conversations which could serve as inspiration for new ideas, and entertain me me with them, as well as exchanging useful information of things worth of learning and retaining. Also, entertaining me with games, such as puzzles....Anything that makes you think, really. Video games too...Exchanging opinions about things I like, and sharing the previous information, and those kind of activities. So, I think that the main purpose would be to entertain me, and motivate me.
It is a shame no one like this exists (I did not get to know someone like that)....So, I guess I do not need friends, if no one like that exists......