I cook the turkey or ham the day before. Then I slice/debone it.
Line your Crockpot with a piece of aluminum foil. Place 1/2 cup water UNDER the foil. Fill the Crockpot with your sliced meat. Refrigerate overnight.
Heat on low for 5-6 hours or on high for 2-3 hours until meat is hot.
This method allows you to keep your kitchen (and yourself) neat and tidy on the day of your big event. There's no trying to neatly carve the bird/ham while dressed up, no spots/splashes on your good clothing, no burnt fingers, your sink isn't filled with the dirty roaster, carving equipment, etc. You'll have more time to be with your guests and enjoy your day.