First off you get a better conversion from solids to liquids because the enzymes that do that have more time to work and you can also build up the amino acids ( or what ever they are) that feed the yeast so you don't have to add things to help the yeast along as it's already there. This boils down to better extraction with less grain used and additives required thus money saved, just a few bucks but now a days a few bucks is a few bucks.
As I said in another post, I did a step mash on my latest brew. I got the same 85% efficiency I always get, so no gain there. And if I can get 85% doing a single infusion, I don't see a reason to do a step mash to improve efficiency.
Secondly you can control things like alcohol content and body of the brew by adjusting your heats and times you spend at the various temps. If I want a higher alcohol content in my stout I can stay at a lower temp a little longer before I raise it up. If I want lower maybe I don't go to the lower temp at all I make the choice. With single step you get what you get. Mash in at 158 and you get higher body and lower alcohol and that's it.
But I can do that perfectly well by manipulating temp and time in a single infusion mash.
Lastly I have to use less water to batch sparge and take less of a chance of washing out things that cause off flavors in the beer because most of my water is already in the turn. I don't have to worry about trashing my ph during the sparge because I'm not doing it that long.
But neither of those things has ever caused me problems in a single infusion. Why should I try to fix something that's fine already?
Expending energy is a matter of opinion and personal preference. What one man calls expending effort with no payoff another one calls time well spent, money saved and problems avoided.
And if you want to do it for that reason, fine by me. But I'm not convinced by your argument that there are benefits to be had.