This is the first time I've heard someone advocate NOT using a two point sling unless actually slinging your rifle. I can see how you'd transition in the middle of a fight to your handgun without just dropping the rifle. Dropping it is fine in some situations, but not others.
Every trainer I know or have really even heard mention this suggests using a quality two point at all times, or occasionally a single point if that very specific need arises. I've never heard them advocate using it only to sling the rifle.
On a side note, I can transition shoulders almost as easy with my VCAS slings as I could with my Gear Sector and MS2 single point slings...almost. I run it relatively loose unless I need it slung and tight. If I attach the rear portion to the end plate instead of the stock, it's even easier and very similar to a single point, though I don't care for the way it hangs.
Edit - not saying there's a right or wrong way, just saying that I don't know anyone that recommends that way.