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
The slide on my Kadet conversion isn't fixed to the barrel assembly at all.
It rides on the inside rails of the gun and moves back and forth as the gun fires.
The barrel assembly is held in place via the slide stop.
Here's one pictured with the slide all the way back.
Since I've never heard or read anywhere that a tight fit of any moving parts does anything but aid accuracy - given the choice, I'll go with tight fit.
The nice part about at least some of the conversion kits is that you do get to make a choice.