BES is for business, BIS is for consumers. There are huge benefits for a company hosting their own BES. Some features include: wireless calendar/addressbook sync, remote wipe, OTA application push, IT policy restrictions (ie disable installation of 3rd party apps), puts you on the company intranet (no need for vpn client, great for remote administration), MDS service, the ability to manage/monitor/control multiple devices from a single console, etc... There is more to it than that, but you can read up on it more here: BlackBerry - BlackBerry Enterprise Server | Integrate Enterprise Applications, Data & Wireless Communication
