It’s a matter of how the shooter wants to promote consistency. If you oversize your bullets, the throat has to do some sizing, which ensures every bullet passing through that particular chamber will be sized exactly the same. Alternatively, if you use a slip fit sized bullet, you can’t necessarily be sure each and every bullet has the exact same slip fit. Does every bullet slide into the throat with the exact same pressure? Is the pressure required for some bullets caused by uniform drag, or by a few random high spots in the bullet circumference (egg shaped bullets, casting mold lines, high driving bands, etc). Lack of lube, excessive lube, out of center gas checks, etc... alternatively, if a shooter relies upon the throat to final size the bullet before presenting it to the forcing cone, how does the shooter know the sizing will happen concentrically, and know the chamber and cartridge case relative position won’t let the bullet press harder against one side of the throat than the other - yielding an out of round bullet leading into the bore?
Personally, I slip fit all of my bullets. Either side is speculation, but I know all of my rounds will chamber and I know they will all be capable of greater precision than I am as the shooter, without leading/copper fouling or gas blow by.
