I use it now to drop off my cargo bike at the shop as the way I get back home. Then go to pick it up by taking it to the shop and riding back with it in the cargo bike.
I use it on transit a lot, especially if there is a questionable availability of full size bike racks on the buses.
All that brings me to the kicker question here, what do you use your Brompton for? I've been brain storming and thinking of other uses. I'm always looking for more reasons to take it out!