It's The GM's Job

The GM being the arbiter of when to make a roll or not is their job.

That can be zero rolls if they like what the players are doing and think they should succeed without involving chance.

That can be many rolls if they want chance to have a larger role in the game.

It can be anything in between.

If can be zero rolls if they dislike what the players are doing and they think they should fail without giving them a chance.

And, for the absolutely stupidest of my readers:*  This decision about how many rolls is independent of the game rules.

It's not a GURPS thing.  It's not a D&D thing.  It's not a Hero thing.  It's not a Traveller thing.

It's a GM thing.

The GM and the players should get on the same page about how often chance is involved.

I tend to roll a bit more often than some because I don't want to railroad the players into being defacto NPC's who only have a little agency.  Letting it to chance is more fair.

If I wanted to control all the characters fully, I'd write fiction...  And you can see from the infrequent snippets of Sabers and Sorcery how well I am doing.

*So stupid, in fact, that I've decided to reply to the comments I've shitcanned until they realize that they are not being allowed to talk.  Not because they're not raising good questions, but because they're being a dick about it and that's contraindicated by the commenting rules.