With regards to retrouvaille, it certainly helps if both parties want to save their M, but I don't think that's the norm. One person generally wants it to work and the other is just lost. When we went, there were a handful of couples separated already and a few that had already filed for D and were just making sure they weren't making a mistake.
For me, I thought it was a benefit regardless of what happened after. Even if the other person doesn't want it to work, or refuses to move forward, you learn so much about yourself that it'd be difficult not to see it as an advantage for any relationship you might have in the future.
