bill - 5:24 am on Sep 14, 2012 (gmt 0)
A Page can be a person, a persona, or a company/business. I haven't encountered limits that I know of in this sense. When I comment as my Page on another Page, that's similar to the interaction individual accounts might have with one another. It's communication among fans/subscribers.
Ads get out to an entirely different set of users who might not otherwise know of your Page. There's still plenty of incentive to use them.