On page 97 of the Versamail user's manual (on the 650 CD), it sez:

"Message removal: Microsoft Exchange ActiveSync removes any email messages from your device that fall outside of the time interval set on the device, as well as any Calendar events that are more than seven days old. For example, if the time interval is set at seven days, any email messages or Calendar events that are eight days old are removed from your device. This info is not removed from the Exchange server."

For historical/journaling purposes (let's see, when did I get my last physical exam...), I like to leave all my old calendar events on my Palm, and I'd hate to have them just blown away.