Sorry, it was from a comment, metrics showed senior devs improved, juniors didn't.

But if you want a sketch solution quickly, know the requirements, and can fix the silly mistakes it's a useful tool. Especially if you are doing something where you are rusty, or are used to a slightly different framework or language.

They are like a super fast but slightly clueless junior, who can hammer out mostly correct boilerplate. Not someone you want unsupervised or training a junior, but usefully in some ways.

And yes, boilerplate has disadvantages, but it has its place.