The Galaxy class starship was designed with the ability to separate the saucer from the stardrive section, so that the “floating city” part of the ship could be left somewhere safe while the rest of the ship galavants off to do something risky. We see this happen precisely once, in the season one episode Arsenal of Freedom. We also see saucer separation deployed for a handful of tactical and or emergency uses (such as against the Borg in The Best of Both Worlds, or to escape the breaching warp core in Generations).
So, this seems like a useful ability to have, and the Enterprise is constantly being sent into dangerous situations. Why not use this ability more frequently?
@maegul @williams_482 I think it would actually be good TV for Lower Decks. A California class might have to visit a Galaxy class saucer that has been left in orbit for a month managing a research expedition or a conference, while the stardrive section got delayed hunting a Romulan warbird.
It just wouldn’t be good television for a show set on a Galaxy class ship. The only way to do a “split ship” show would probably be to mainly follow characters on only one half.