It will help rollout control no more and no less than crabbed to un-crabbed round-out and touchdown. Again asymmetrical thrust is to assist you with crab, more accurately, needing less of it during the approach phase. As you prepare your round-out and flare you usually just start applying rudder, which takes time to react right? Well now you are slowly lowering the engines to even and to idle together, which takes time just the same. Both I suspect (as I haven't flown jets you can correct me here) with only a 5 percent difference a matter of a second or two, just like rudder.

Again, I suspect it isn't in any procedures because of the KISS rule. As you can clearly see more is going on in this type of approach, round out, and landing than a typical one.