For posting:
- invitations to games (you can also use the New Game menu)
- information about upcoming tournaments
- discussion of games (please limit this to completed games or discussion on how a game has arrived at a certain position ... speculation on who has an advantage or the benefits of potential moves is not permitted)
- links to interesting related sites (non-promotional)
Justaminute: Actually currently the most common cause is that two chess bigshots find it in their common interest to have a draw outcome, then go through the motion of having such a repetition early in the game to avoid the wrath of the referees.