Quoted from ForceFlow:Weight. The cabinet body isn't quite as heavy when you remove the playfield. Less weight means it's easier to haul up the stairs. And since I've already disconnected everything from the backbox, disconnecting the remaining cables for the playfield is fairly trivial.
Once the cabinet is up the stairs, I put the playfield back in.
I've done this a number of times both for stairs and for narrow doorways. Hate taking backbox off and pulling all those cables + the pf coming out is usually damn heavy and can be sketchy. However, it's near impossible to go up stairs with everything together with 1 person and traditional handyruvk. I wouldn't go down solo either.. while it's a breeze to move the empty cab. Bigger wheels always help with stairs