I would argue that "advantage" in your scenario only applies to the employer, who doesn't have to provide space for two people. For those who must now share a space, I would consider this a disadvantage.

It makes sense for a couple of self-employed startup founders :)

As someone who has a desk at a co-working space, I'd want to murder you after 3 hours. It's not really an appropriate place to spend 8 hours a day talking to each other:)

Noise-cancelling headphones, perhaps? There will always be quite a bit of noise in an open-office coworking space.