On the basis that a lot of pros are using sprayers to do whole homes you have to assume its cheaper otherwise they'd be rolling it. Now thats probably easier when your ceiling and walls are all the same pot of paint. For a room with one feature wall you'd do that first and then mask it off. Doing a single room that's got carpet down, rubbish in the way and so on I imagine change the equation slightly. But when you see how fast a room can be done and the finish you get, you're only masking most of it once. Once the floor is protected you don't have to do it again, once the switches and sockets are protected you don't do it again, both of which probably need doing anyway for a brush and roller The only extra masking to add at any point to to protect the woodwork once finished and then any feature being done. Not hard when you're using the rolls of film or paper with tape on them already.
When you want 3 different shades of not quite white on the walls and ceiling it might be more work.
I'm going to be doing my daughters new room next week hopefully. White ceiling and walls, pink feature wall and white skirting, window sill and door.