The square format works great with portraits. Look at Avedon or Penn's work. Both used an 80mm Rollei in the 50s and 60s. Nothing wrong with 3/4 length portraits. Avedon and Penn shot close enough to distort features and it worked for them. Also, 50/60s Rollei glass often gives a certain rounded 3D look which is very interesting.
A large part of David Baileys work in the sixties was shot on Rolleiflexes, and he still uses them.