Definitely a good thing for learning, at a comp, in practice, anytime.
Not good a as a must-have requirement to run a comp.
I am involved in training our drivers & use it wherever possible. The setup can be just a Handycam on 6-inch tripod to review later on awkward sites.
When I pay my entry, I expect a driver to be competent at my level of skiing. If a driver needs to practise, I'm happy to ski for them, but don't like to pay for them to use me as a punching bag.