Its just a showy thing. The more rep you get, the more green bars you get. If you hate someone you can give them neg rep. Then if they step out of line and brb is asked to ban them, he can see what their rep is like ans **** on them
If you want to have a laugh with the rep thing MIGHTY, visit the rep brothel on the Toon board. If you rep the ones that have the most rep, when they rep you back, you'll soon get over the 1000 mark.