I clean mine spotless because that's what my dad taught me before he passed away, and when I got drafted the army was the same way. We had M14s in basic, and we fired 4-500 rounds a day sometimes. Our job before dinner was to get that pogo stick immaculate. So it's just habit I guess.
However, some of my guns don't get shot much and I feel that if they sit for really long times I don't want anything in the bore that attracts moisture.
Also, and I'll bet I'm really going to stir it up here, I was taught many years ago by a competition muzzle loader to wax my guns.
That's right, Johnson's floor wax. The stuff in the yellow tin. Three times. Wipe it on, let it haze, and wipe it off.
I have something in my blood that will rust anything. My dad wouldn't let me handle his micrometers. I can leave a thumb print over night on a piece of raw steel.
Since I started waxing my guns, I've had no rust issues, and they clean up easier after I've shot them.
It doesn't seem to have any effect on bluing or case hardening, as I have some old rifles that I've been doing this to for years.