creating a new "Access Web Database" or publishing an existing Access Database to SharePoint 2010

What are the limitations of either creating a new "Access Web Database" or publishing an existing Access Database to SharePoint 2010?

I'm trying to decide if i should publish an existing Db or create a new web DB. What can or cannot be done with Access Web Databases? i spent a couple of days now trying to find these information but nothing of importance came on Google, Any ideas?

thanks,