The more points you have indicates the more time you have with nothing more productive or satisfying to do .

Ditto on what others have said.
It encourages people to actually interact with members (even if all you do is click "like" on other peoples posts), and it helps weed out the scammers and fakes.. (by the time a person has made it to level 6, you pretty much know they are for real)

It raises your levels,interact with posts,join a chatroom for discussons,let the people know more about you,create thought provoking posts.

Points mean prizes! For every thousand you get 10% discount on fuel/gas at your local station, for every 10,000 you get an amazon gift card and for every 100,000 you get to become Pope

Or you get certain (secret) privileges up to level 8 when you get a rather nice t-shirt and pen

The points system here is mostly for fun, but it also serves to prevent spamming by people new to the site. As you gain levels, you also gain privileges (e.g., the ability to directly message other members). You gain points and increase levels by completing your profile, making posts, commenting on posts, liking comments, etc. Don't get too bogged down by the points and levels and just enjoy the site. (Although, when you reach level 8 you're eligible to receive some merchandise. I think they give you a t-shirt and a pen. When I crossed the threshold, though, they didn't have pens yet.) Welcome and enjoy!

"As this site is completely free, we have to put limits on contacting others to avoid spamming. We do this with levels based on a simple point system where each activity is assigned points and members level up once they reach a certain number of points.

Levels are mostly a way to help identify and reward those who contribute to the growth of the community. We also give more access and benefits depending on level. For example, posts by new members are reviewed before they show up to others (except on the profile page where they go up instantly) whereas members of higher levels have their posts go live instantly. Also, we let members with higher levels contact others more than lower levels.

Note: points are counted as soon as you upload or post things. Your level is updated when things are reviewed and approved on the site."

[agnostic.com]