drills hitting shots with one hand are useful, yes. Left hand only really teaches the proper lead forearm rotation through the shot, and right hand really teaches the 'throw' and extention through the shot (as well as right wrist back, ride the rim). It can also help you get your right shoulder more 'down' on plane.
I would focus mainly on smaller swings, hip to hip at most - even just chip swings are enough to get the proper right hand feel.
Best to drill on a rotating basis...
Hit a few with left only (no more than 4-6)
Then both hands
Then right hand
Then both etc.....
I also like to throw in the 'swinging a club in each hand, same distance apart' drill in this rotation. One of the best drills you can do IMO.
The downside of the drill with one hand only, is that it can encourage you to get out of synch with the chest a bit (the main reason to only do hip to hip) - to be 'disconnected' a bit. Just be aware of that as you do them. Hands and chest must stay together.
