We use several custom statuses to separate things that are pending waiting for user response, on hold for a specific amount of time, or pending a third party. It would be very nice if we had the ability to "map" these values to one of the system categories of Open, On Hold, Resolve or Closed. Right now, we may have 50+ tickets pending a change request, but the Dashboard will only show 2 On Hold (in the default Pending status).
The reason we separate those is to allow automation rules to function differently. On Pending, the ticket will eventually close if we don't hear back from the user, but we do not want to close anything in Pending Change or On Hold.
Another use case for this would be to separate Closed statues in line with ITIL resolved categories, such as Fixed, Not Fixed, Closed with Workaround. Right now we can't really use those, as the system does not recognize them as closed.