Well, that would depend on the restaurant. When I called for a reservation at Cape May Buffet for 11 people, I was told there were only two table for six and they were across the restaurant from each other. It just depends.
Most of the time, if your party is large, your reservation will be "split" between several tables. For example, my dinner for twelve at LeCellier was really three tables of four next to each other (which they did push together for us). If your party is too big for the regular dining number to handle, they will refer you to group sales.