load work is done off hand or off bag?
Shooting offhand tests your accuracy. The better, ie: more accurately the load shoots, the tighter will be your offhand grouping. Work up a load, then shoot it offhand.
People who think "it doesn't matter, because I'm shooting offhand" usually are not competitive with those who know it matters.
The necessity for the 'best' accuracy is not important for many people & that is fine. Each to his/her own.
However, if you want the best accuracy from your rifle or smoothbore, you must use a rest for load development.