Whilst it might work out that way with lean bailout on the left and rich deco gasses on the right, I would never ever not check the cylinders before breathing from them.
The problem, IMHO, with all of these prescriptions is they lead to problems. For example on a deeper OC twinset dive, I'll have 3 ali80s which will be the 50%, 80% and a bottom stage with backgas. Once down, I'll switch to the bottom stage - checking which gas it is first. Use it until mostly consumed, then switch to back gas. I keep that on the RHS as I find it easier. When getting to the first deco stop I'll switch to the 50% on the LHS, but check it first, even if I know it's the only cylinder on the LHS. Same with switching to the 80% (I don't like 100%, too hot) on the RHS.
If, when diving with two stages on the RHS, I need to do a donate then it'll be from my mouth and close in to the other diver - there's plenty of hose for them to breathe; I'll scoop up my backup. When settled, then I'll unclip or faff with the other stages to free the longhose all the way. It really isn't difficult.
Obviously if it's the rebreather it'll be a donate of the bailout reg. If the crap's really hit and I need to donate at deco, it'll be the reg in my mouth and I'll go back on to bailout.
BTW I sidemount bungee the bailout and deco stages back to keep them under control during the bottom phase.
Everyone's different. Let's enjoy that.