Users have multiple sessions in 2003 file server

Our office uses Windows Server 2003 R2 SP2 for our file server.

In the File Server Management console, under Sessions (Local) many of the users have multiple sessions listed, most of them on the same workstation, each with different Connection Times (durations), ranging for one user from 5 hrs to 20 days.

I have found that a) users logged out of their workstations still retain sessions on the file server, and b) closing one session will end all sessions listed for that user.

I'm currently investigating issues with some files taking extremely long periods of time to load (we've got a fully gigabit network in our office, very fast, very low latency) and am wondering why multiple sessions are listed and what the significance of that is, and if this may have any bearing on possible periodic sluggishness of the server.

Also, is there a way to configure the server to end each session as the user logs off their workstation?

UPDATE: I found the source of the file slowness. Excel patch 2502786 caused slowness when opening network files. The questions regarding multiple sessions is still valid, though.