Interior Designer Rose Tarlow is very particular when it comes to sofas, “I never use two seat cushions because three people won’t sit on the sofa…”
I didn’t give it too much thought until I ended up with this sofa:
Notice it has ONE cushion. The design offers two affordances: the choice of where to sit and the number of people who can sit. By contrast a traditional three-cushion sofa constrains those choices. A two-cushion sofa offers ambiguous cues on how many can sit and where they can sit.
In the Design of Everyday Things, Don Norman said;
“…the appearance of the device must provide the critical clues required for its proper operation—knowledge has to be both in the head and in the world”.
So judging by this principle, single cushion sofas are better than three and two-cushion sofas. Though of course those sofas have different affordances like easier clean-ability.