My sister is into this and has been for many years. Well before it became a well known concept. For her it isn't a sexual thing, but a love thing. She likes the feeling of falling in love, but without the kids and a dog thing. She has got a life partner who's also into it, (obviously). But they are mostly friends and have good sex. It's not a fear of intimacy thing, but rather a chemical thing. As she puts it, she likes the chemicals that get released when she's in love, (oxytocin). She used to be a scientist, so she should know. When the chemicals die out she goes to the next one. She has a life partner since 20 years, so she has everything else one could expect from married life.

The only reason I'm not into it is because I'm not strong enough. I couldn't handle the emotional roller coaster. I would if I could.