I mean, as far as I can tell, the rule is an attempt to get rid of paid line sitters. The intent of these tickets was to allow people who couldn't buy resale tickets the opportunity to buy cheaper tickets. The line sitters (SOLD), regardless of how nice they are, are just another way for people with more money to see the show, and screw over people with less.
That's what I think the intent is, so I think if you're waiting in line for pair tickets, the person you are seeing the show with can swap out with you. Does this sound accurate?
Obviously it seems like a self-policing thing. In the end though, it sounds better for fans who can't afford line sitters. there's potentially shorter lines without SOLD being able to swap out for people who could afford them. Sucks for their clients, but that was not the original intent of this line anyway.
I'm finding it hard to sympathize with the SOLD guys, honestly. It was just a way to make money off a system that was designed to give those with less money an opportunity to see a show - and I'm sure I don't need to address the issue of how inaccessible musical theater is for the less-wealthy compared to other forms of art.