Low cadence (sub 60) at high torque (typically under/over threshold power) training is definitely a thing. Benefits:-
1. Helps massively when you encounter hills that are steep enough to force you into that kind of low cadence/high torque threshold effort
2. Activates different muscle groups eg. uses glutes more than high cadence
I'm a big believer in training a very wide cadence range, while generally trying to push up my average cadence. So I train at everything from 55-130+ rpm, while my average is typically in the mid-high 80s.