It depends on what kind of adverts you wish to have.
if you have any deals going with adsense and google or any other advertisment thingy ma whoser ... then they require that you embed some advert on your site... well to embed these adverts you can use:
your homepage message (admin panel-> display -> generalities) your widgets ( admin panel -> modules -> forum and portal widgets)
If you want an affiliate program... like you share links with other forums... you can also use the homepage menu and the widgets...
Its really for specific adverts that I can control, I dont want to be flooded with ads from the likes of google etc.. say if I had mine own add I wanted to put up, is that possible?