Shadowman,
It's just a miracle if a base(s) precisely mates with the action the way it's "intended" to. I mean it's just dumb luck if it does, period. Bed it and be sure it fits. Using a dial indicator is the only way to measure the flex (deflection) caused by the misalignments while screws are torqued. Depending on which screw(s) are torqued and where the deflection is measured, this is what tells you where the gaps are that need to be filled with bedding. It also tells you which screws can and can not be tightened during the bedding process without inducing flex into the base. And no, the base will do the flexing and the action will not. That's not to say the action isn't becoming stressed as a result, just that measurable flex is not taking place in anything but the base itself. Most of the time the amount of flex is quite alot too, either bowing the base and bringing the rings closer together at the top or the opposite, not to mention twisting the base.
I try to find a screw to tighten that secures the base with no induced flex and hopefully it's a screw in the front that helps keep a more forward cant to the base allowing more internal reticle adjustment. In this case a rear screw is just used to align the base, screwed in and stopped just shy of deflecting it any... of course an indicator is used again during this procedure. The base is secured to the action just as it will be bedded, rings and scope attached after a light check with a lap bar. Scope internals are zeroed then rifle is carefully boresighted to confirm this setup will indeed work and vertical adjustment is in the lower range (I like 5-10 MOA off the bottom in most cases) and that windage is very near zero and acceptable. Remove and bed it.
Is there a measured accuracy improvement? Depends. I'm not willing to test that on every rifle to find out, and by how much. The very little time it takes to bed one is worth it knowing everything is true, solid & stress free... as is the whole rifle.
Harold Vaughn's book "Rifle Accuracy Facts" will give you even a better understanding of this and a whole lot more pertaining to it.