It was a post on Box o' Truth that brought this up:
I am prompted to ask: at what point do you sacrifice accuracy, just to feel like you’re shooting the gun in a realistic manner? If you tell people how well you shoot, but you do all your shooting in this odd way, are you being completely honest? If you had to shoot somewhere other than the range, would you have all this crap with you, and would you use it? Maybe it’s better to buy a machine that fires the gun. I have one, although I haven’t used it yet.
I know most of you are quite familiar with the matter, but on the chance there's someone reading my stuff who's not, I shall now pontificate:
A solid rest is invaluable for a number of things with a rifle:
Adjusting sights so the point of impact and point of aim will be as you choose,
Testing ammo to see what works best in your rifle, or to test a new handload,
Making sure a scope is mounted with the crosshairs(or whatever reticle) exactly square,
Giving a new shooter a comfortable way to get started.
In the first three, the common thing is trying to reduce human error as much as possible; it's not to test your shooting skills, it's to test the sights/ammo. That means a solid rest that keeps things as stable as possible. You're still doing the aiming, your breathing and trigger squeeze is still very important, but it removes or reduces the errors that can be caused by any kind of sitting/standing/kneeling/prone position; very important when adjusting sights or testing ammo.
On sights: one thing a lot of people don't realize is that it's not uncommon for a rifle sighted in from a solid rest to have a different point of impact when it's not on the rest. As a 'for instance', my Model 94 Winchester: shoot it from a solid rest, receiver or forend on the front rest, stock on the bag, to test ammo, BUT when you take it off that rest(for instance, put your hand between the forend and rest, or shoot it from sitting position) the point of impact will be several inches below where it is when shooting from the rest. BIG difference as the range stretches out. So once you sight in from the bench, you need to get in field positions and shoot to make sure if your POI shifts. Shoot from prone with a sling, you might find it hits a bit(sometimes quite a bit) off, usually low and to the side, from where it hit off the bench.
That's my short & dirty version: feel free to make corrections. And take a look at the Box o' Truth to see how he shows it.