I thought this was going to be about all the small hallways in Doom where you have to close one door before opening another - this was done so that the engine would never have to render more space than 1 room at a time. I don't know if that's true, just something I've often heard repeated.
I played Doom, Doom 2 and Final Doom all the way through about 20 years ago - I can’t recall a single instance of this kind of level design. Doors stayed open once opened. Maybe it was done with corners/sight lines instead? To be honest I remember some vast areas rendered, especially when accessing secrets.
