From an era when real photographers used sheet film. None of that new-fangled roll film 120 or 35mm nonsense, heaven forbid. A lightweight camera was a 4x5 but 8x10 was where it was at. Actually, real photographers still do 8x10. Digital is for pretenders.
I read an interview with a famous portrait photographer many years ago (when everyone still used film). He strived for a very formal, old fashioned look in his pictures. For that reason he only used a 4x5 camera. Not for the extra resolution, but because the setup placed his subjects in the right frame of mind. One look at the rig and they realized that the portrait session was a very serious affair. The slow process, with the photographer ducking under a cloth to take the picture, must have helped as well. Apparently even a medium frame camera made the subjects relax too much.