It saves on rewiring stuff. Maybe there's only one person talking today. Maybe they're using PC A, or perhaps they're using PC B instead.

Or maybe there's two people in the room, each on different channels altogether. In this case the other person is just uncorrelated background noise instead of a persistent echo.

Or, in-context: There's two people in the same room, both talking on the same Discord channel.

Anyway, audio routing is useful. Being able to route audio with two different PCs is a pretty neat feature of the rodecaster.