Being ever so slightly serious, doesn't it depend on the criteria? I mean, this is a swinging site, so the attraction for the "swing" may not be, in fact almost certainly isn't, the attraction for the life partner. It's something else, the missing bit.
If you're married to a nice guy but you've always fantasised about the boy in the 6th who was VWE and everyone talked about, that would be one of the criteria to swing, but a life partner brings a whole load of other factors, romance, income, trust, a pal.
A lady said to me last week that one of my attractions was that I knew how to talk to women. Actually I was not greatly thrilled by this news, wishing somehow that my attraction was a good deal less cerebral, but with my body that's not likely and so I do need to have some talent. If talking to women is mine - so be it. Writing this, I recall that in my 20's I always used to boast that I talked them into bed, I'd forgotten. Maybe she's right.
Pity though. Useless talent on SH.