What are the rules for?

[Micah Sweet]

Somebody's probably written a TTRPG focused on simulating trade, where you might be operating a vessel visiting different ports and exchanging goods of various sorts. If so, weight seems like one reasonable constraint in terms of determining how much cargo (and other stuff, like food and water etc) you can actually bring along.

I can think of at least a couple games where what you're describing absolutely exists and is important.