Depends on the dog.
Whippy; Allowed on the sofa, all the time under all circumstances, except occasionally for her own protection if there are excited, bouncing children all over it.
Devil Dog; Allowed on the sofa when there are no children on it or foster dogs or when I am in the room.
Current Foster; Started being allowed only when Devil Dog was not there first, but became so possessive of the sofa she is not even allowed in the room the sofa is kept in, except for when doing training, alone in a room with only me and her . We are working on learning "off" (the sofa) "on" (to the sofa) "bed" (self explanatory) and that allowing people near things she covets (such as the sofa, bed, pet bowls etc. brings extra goodies not threats. She is being rehomed to an adult only, dog experienced home.