It's all about consistency.
The more even you get the fit, the more consistent the action is going to work.
That may be less true with the Kadet Kit design than some kits, as the "fitting" process mostly has to do with getting the lower lugs slightly narrowed to allow the kit to fit on the frame
The barrel itself is fixed to the slide and the slide is held relatively securely by the slide stop and doesn't move much (if at all) when the weapon fires -- just a small section on the slide at the back moves. It is, in effect, a fixed barrel system. The barrel and the sights never change their alignment, so accuracy should be fine unless you're using a Ransom Rest.
In my experience, kits that fit one gun, when moved to another, don't demonstrate a noticeable change in accuracy or consistency -- but it could be that my experience isn't broad enough.
My Kadet Kit shot so well when mounted on my 85 Combat with which I first used it I realized that I wasn't going to shoot it in another gun. It worked on the 85 Combat frame without fitting, straight out of the box, and some people have had similar experience with their 75Bs,
My kit would NOT work with a couple of different pre-B 75 guns, but that was due to the fact that the pre-B hammers (on my early pre-Bs) were too wide to fit in the slot at the rear of the Kadet Kit slide, which kept the hammer from hitting the firing pint. The Kit would have require some tweaks to work on the 75B SA I had at the time, and it wasn't even close to fitting on a number of different CZ clones for a number of different reasons.