Don't split the party!

There are several valid reasons not to split the party. GMs have a lot on their plates during the game, and PCs being all over the place increases the cognitive load. GM can’t split, and the players won’t explore the dungeon faster. There’s also a matter of time spent on “I’m relaying the information I’ve just heard to the rest of the party”.

On the other hand, there are valid reasons to actually split. It may help shy players to get more spotlight. It may be required by narrative, e.g. some of the PCs can breathe underwater, but some don’t; some have vac suits, and some don’t.

TTRPG is a deeply human experience, and as such, there are not many hard and fast rules.