Contacts. Personal Journal. Bookmarks.
Take outside forces (like a mandatory disk encryption software that scrambled hard drives occassioanally), add angry users, stir. BOOM!
Put the three sets of information all in the same file, the mail file, as a default (ok, option). Users expect that all of their data is on the server and backed up, even when you tell them otherwise. They don't want to manually Synchronize with silly action options, nor deal with replication, if they don't need to. Admins also need a simple means to locate information on the server for related support issues.
Yes, you can use Roaming to put files here or there, create more replication overhead and support issues for your users, and make running Notes on Citrix a mess, but why bother?