You can share meals (use one credit to feed two or more) at almost all of the Table Service restaurants where you order from a menu. The one exception is Via Napoli which strictly enforces the dining plan and requires each person to use a credit. You can use the credit on the individual sized pizza or a non-pizza entree, but you cannot combine credits to order the larger size pizza.
You cannot share and everyone will be charged a credit at buffets, All You Care To Eat family style meals (e.g. 'Ohana, Garden Grill), fixed price meals (e.g. CRT, Akershus), dinner shows (Hoop De Doo, Spirit of Aloha Luau, Mickey's Backyard Barbecue), dining packages (e.g. Fantasmic, ROL), dessert parties (e.g. MK. Star Wars, ), special events (e.g. Dine With an Imagineer, F&W special events) and the Family Platter at Whispering Canyon Cafe.