Based on someone's post, I had this vision:
I'm in line with two kids and decide, "OK, this is nuts - I'll go ahead and pay the 15(?) dollars to do the LL$." So, I get out of line and go to the other queue. Meanwhile, someone else sees that and thinks, "Well, if he's going in that new line, why can't we?" (but doesn't pay). All arrive at the CM and I can scan in but they can't and they become frustrated (and, what, start at the back of the line?). Or, Guest X says they bought it and show a screenshot of paying - but it doesn't show up in their MDE account (maybe the system glitched, maybe they're using a fake thing, IDK). The CMs get to deal with that, plus the other guests, etc. What if a family doesn't comprehend it and they buy G+ or LL$ for the adults but not the kids - how do the CMs help solve that problem in the moment?