I won’t end up single-bagging a bunch of stuff that could be bagged together (e.g. if they scanned some window cleaner, they bag it separate, not knowing that some dishwasher detergent is coming that it could be packed with).

Not that it is foolproof but unloading your cart in an organized manner helps with that. Though maybe you’re talking about helpless baggers, I’ve seen plenty of both clueless baggers and customers who toss things onto the belt willy-nilly.