Pros:
Automatically backs up user data to the server whenever they log out, so that the user doesn’t have to remember to do so.
Allows users to log into multiple computers. This works great in an environment where people don’t have designated desks, such as an open lab.
Cons:
Security issues. After the user has logged on, a copy of their profile is left on the hard drive. If the computer were to be stolen, this data could easily be compromised.
Slow login times. If a user puts too much data in their profile, it could take a very long time to transfer all that data whenever they log on or off. This could lead to profile corruption.
Bandwidth consumption. Large user profiles take a lot of network bandwidth to transfer data back and forth. Much of this is amounts to wasted bandwidth since many of the files and data transferred are not accessed every time the user logs on.
Maintenance issues. I regularly have to clean old profiles off some computers because those profiles left behind fill the hard drive so much that they prevent other people from logging in. It’s also a fairly regularly problem to have to rebuild user profiles after data has been corrupted during transfer.