This is how I think this works, but I'm no mechanical engineer...
Imagine the intermediate shaft and gear shifting it's contact patch with the cam gear up and down by that.030" in relation to each other. Much like setting up a rear end, there are certain ranges of movement that once exceeded begin to accelerate wear of the gears, especially one made of much softer material.
In a running engine, the intermediate shaft does move up and down within that .030" range as the cam and gear speeds change. Under increasing RPM, the intermediate shaft is forced down onto the bushing face and visa versa. This widens the gear contact pattern which, after a point, accelerates the wear of the gears especially the softer ones.
Limiting that travel by using a 1/2" locking collar would result in the two gears maintaining a much closer gear contact pattern that results in less overall wear on the soft gear. Think of a pinion gear in a rearend moving in and out excessively beyond the normal travel specification. That is no bueno. You can often hear the backlash when driving.
