Off topic, but this post piqued my attention. What era and which 4 railroads did they choose to model ATSF, Colorado Southern, Mopac, and Rio Grande? I intend to include the C&W and Rock Island also.
On topic, Necessary, "no", but I think everyone has pointed out the good arguments for having staging. My first was in 1980 before it was a "thing". I put three tracks behind a backdrop so I could keep the trains there without cluttering up my pretty scenery on the front of the back drop. Since then I've included it whenever possible, and follow the mantra - one cannot have too much staging. The Greeley museum started with 7 on each end. Added 2 more in the isle on each end. That sucked up all the isle space so came back and added 4 more "through" tracks (equivalent of 8 of the above) and 6 stub ended ones under the upper deck of the layout. And we still have issues putting trains on a off because there isn't enough room.