>>51132814As others has said, done right, they give you early access to interesting mons, like Munchlax and shit.
The issue is there is tons of baby bloat from Gen 2 and then when they added say, Chingling, it wasn't exactly for an interesting pokemon in the first place, or you have Mantyke which you can only get at the 8th gym.
I think SwSh was the only time it was really effective for team building. But that's anecdotal.