The ability to track vehicles quickly, easily & efficiently in real time from anywhere with any internet connection! I also like that it's relatively inexpensive compared to other companies out there (e.g., SafeTrack).
It would be nice if you could customize your dashboard for each department or client so they can see their own data without having to login separately - but this isn't too big an issue since most people aren't logging into multiple dashboards at once anyway. We use TracPoint primarily as our main log-in point when we are away from home/office. This makes sure all employees have access to information about work locations while traveling.