The other players must be ready to cut if a poach happens or the main cut gets stopped. But if players are spread out like in a long stack, then typically only one or two players will be in a good position to cut, and it is easier for each player to determine whether someone else is cutting. If you are in a short stack, then there are 8 or 10 other players in your immediate peripheral vision, and it's hard to tell what each of them is doing and whether any are cutting. If there is only one other offensive player and his defender that you can see, any motion you detect is likely to be a cut. The long stack is better suited to a rigid or almost rigid sequential offense.
Many teams are fairly strict about having plays go from handler to handler to middle to deep.
The short stack requires a little more concentration and familiarity and discipline, but is better for an established team that doesn't change much from year to year. The long stack is easier to learn, it is better for a sequential offense, and an individual's role is defined pretty much by the position that he is assigned to. In the short stack, the role for each player depends more on other things like his abilities and the called four person play rather than where he lines up in the stack. The typical stack with begin with a handler 15-20 yards from the disc, followed by the other handler, the middles, and finally the deeps, with everyone four or five yards from the nearest neighbor. Typically, the first player in the stack cuts first.