BDSM can be just light fun engaged in with one's partner.
On the other hand, some forms of BDSM---particularly scenes---can allow us to to escape ourselves, particularly the aspects of ourselves which need to be active in the complex world outside of the dungeon. Pain, and the intense focus on the here-and-now, reduces our need for all those aspects of ourselves, and much of what we are can be released into the background. Thus we shrink ourselves down to a minimum and the task of being us becomes much easier.
Baumesister and Boden note that "... it becomes clear why shrinking the self may be desirable and beneficial for modern individuals. The self is a source of stress, and stress is reduced by interruption, so modern citizens will be much better off if they can forget themselves now and then. A temporary escape is all that is needed, but it is needed."
Both the light fun aspect and the escaping from ourselves aspect of BDSM can simply be forms of recreation. Afterwards we might feel refreshed, as if our batteries had been recharged, and we're ready to go out and confront the world again.
- [Baumeister1994] (p. 149)