Swinging is an activity both spouses do together. In swinging co marital sex enriches marriages in all areas, especially in the erotic sector. But swinging evidently cannot very often save a poor marriage. Some
swingers feel that a weak marriage probably will not survive swinging and that perhaps in such cases couples shouldn't swing.
Even if the marriage is strong you want a little bit of variety; you don't love your partner any less but you want something a little bit different. Just the newness of it, the experience with another person is very electrifying. It charges you up. It gives you something that you just can't get from someone that you know very, very well even though you may love them dearly. You just can't it under those circumstances.
With swinging you have the opportunity to meet other people. You go with someone and have a sexual experience with someone else and no one thinks the less of you for it. Swinging also helps you explore your own sexuality an aspects of which did not surface in your married life.
And if you're free enough to allow your partner to have the same freedom, then this is fine.
As far as many swingers are concerned, it is a good way to charge yourself up once in a while and get yourself an experience that you just can't get any other way. Your experiences with someone else enhance your own sexual experiences with your own partner. There are just some things you can't do with your own, you have to get them from outside sources.