Fair enough. I'm not trying to convince you to do it more often; I can see how in a group where the players don't care about each other's characters and half the characters don't have goals, splitting the group up too often could be a recipe for boredom.So Bob goes of to infiltrate the Acme warehouse. He's going on his own, he really wants those new Acme Rocket Powered Roller Skates. While we're resolving his infiltration, what is everyone else doing? Sometimes it's fun to watch others play through something, which is why I no longer send people off to play pool when we split the party. Other times? It just gets boring if it goes on for too long. Also depends on the group and what individuals enjoy. Some will enjoy the show, others won't. I have to balance based on what people actually care about, not what I think they should care about.
What I'm saying is that in a group that does care about each other's characters, and where the characters do all have goals, splitting the party and cutting between scenes can be a very effective technique.
I would say that if people can go away and have a game of pool while the other scene is going on, that GM is not cutting between scenes quickly enough. I normally progress each scene towards a dice roll - a stealth check, a persuasion check, etc - and then switch back. It should be quick cuts like in a movie or TV show.