Well mainly I'm thinking of myself and 99% of the population when I say it might not be the best idea.
Well probably neither is a homosexual relationship a good idea if you're heterosexual... The fact it might not work for you isn't really relevant.
Some people, fine, it might work well but I just can't see it on a larger scale. Doesn't it just allow a guy to have many sexual partners while maintaining relationships with all of them? It's not really cheating assuming everyone involved is aware, but I just can't see it.
Doesn't matter if you can see it or not, there are various people in these relationships already and it works for them, there are various combinations and ground rules.