Banner Advert Server

Could anyone give me a reason why someone would pay for a banner server/service when google adManager is now free?

I am trying to understand whether there is a market for a simple PAYG banner server product.

Thoughts appreciated

Not everyone wants Google, a direct competitor, to know so much about their advertising deals.

Most paid adservers have much more sophisticated targeting tools than Google Admanager. Which is not to say that Admanager isn’t a fine product and will handle everything that most publishers want to do.

Not a good one. Unless your site doesn’t meet google’s restrictions(Adult content and such)