You can share (use 1 TS credit to feed 2 or more people) at most TS restaurants where you order from a menu. We have done it at many restaurants. The only TS restaurant that has consistently enforced strict rules when using dining credits is Via Napoli. At VN, you cannot use one credit to feed 2 people. With a credit you can order the individual sized pizza, but you cannot combine credits to order a larger pizza or you can use a credit to order a non-pizza entree.
You cannot share and everyone will be charged a credit or pay out of pocket at buffets (e.g. Biergarten, Boma, Crystal Palace), family style all you care to eat meals (e.g. Garden Grill, 'Ohana), the dinner shows (Hoop De Doo, Spirit of Aloha Luau, Mickey's Backyard Barbecue), fixed price venues (e.g. CRT, Akershus), dinner packages (e.g. Candlelight, Jungle Book, Fantasmic), special events (e.g. dessert parties, F&W special dinners and events), and the Family Platter at Whispering Canyon Cafe.