I think it varies. If your offline promotion includes CD's then you are just going to be promoting that one room. However if your site is a niche site to one area or college campus, then you would be better off to promote the entire site and let individuals enjoy all your content and make their own decision.

One example where I would just promote one room is if I am sponsoring a $10 tourney just for my list of local players and buddies in the area. I'll usually make a flier and distribute it to everyone I know and post it all over the place. Instead of a bonus code I always just register a domain name that has something to do with my tourney and either build a splash page or have it forwarded right to the site.

Private tournies are a great way to bring on new players to a site when promoting offline, or even online for that matter.