I think it is purely cost/benefit analysis. The main pro is that the people can access their files quicker. A lesser benefit is that an outage will now affect fewer people. The cons are that you now have an additional server to administer, replicate to, backup, etc. You also have more hardware that can go bad. You will need someone on site to change backup tapes, as well as be your eyes and hands when something happens and remote control software isn't available. Bandwidth is cheap. I always vote for WAN access (with a strong enough pipe) unless you have more than 40-50 people at a site.
This was first published in July 2002