I have found that when you pre-pull and store into bags or pans, the meat will dry a bit, of course you can save the au jus from the smoke and pour over to bring it back to life or use your sauce of choice or simply pour some apple juice on the meat while reheating. I always do more butts than needed so we can freeze the leftovers and enjoy later, and it is good that way, but never as good as it is when it is freshly pulled. Another option I have started using is even if I am precooking (a day or 2 days before a party or such, I'll just leave the thing as a whole in the pan covered in foil in the fridge, then pop it in the oven (at 300 degrees or more) an hour or 2 before I need it, then pull and enjoy. It retains so much more moisture and is fresher to me. I have even pulled apart maybe half a butt one night, refrigerated and pulled the other half the next night and it still is almost as fresh as if it just came off the pit.