I do not cater, but I do serve large groups of people at parties, work functions, etc.
Since I normally cannot cook the day of, I cook/pull in advance and store in ziploc bags.
When I warm up the pulled pork (normally in a large crock pot), I add a mixture a 25/75 BBQ sauce and apple cider to keep the meet from drying out.
I always serve sauce on the side.
My two cents.