"Power exchange" in
BDSM or leathersex refers to the
consensual
interplay in control between participants in a '
scene'.
While nominally the 'top' (or dominant) is in control at all times,
because the exchange of power is based on consent, that control
actually exists only in a narrowly defined context ... and it has
limits.
If the scene in question has safewords in place then the bottom
(submissive) can stop the scene at any time. Even in a scene between
players you aren't using safewords, the top is always reading the
feedback / experience of the bottom, thus the bottom's state is always
setting bounds on the tops actions.
Whether a scene is based on SM e.g. flogging or sex-magic work
e.g. fisting or DS/role-play, power exchange is an exercise
in balance. The top(s) may experience pleasure from alternately
pushing his or her partner(s) to some edge and then letting off,
allowing stamina to rebuild and re-assaulting.
The pace of this 'dance' can be hypnotic, the pace of SM play
is (not surprisingly) like the ebb and flow of any good sex,
building repeatedly closer to (or through multiple) orgasm(s). The
rhythms, like those of music often echo the body's rhythms of
breath and heartbeat.
This is the difference between 'domineering' actions in which
basically there is (potential) energy on one side of the
equation, it's static (and not very interesting) it may indeed
be quite draining to put energy into maintaining one-sided balance
of power.
This is the essence of leathersex, the power exchange between
players is dynamic and can build new energy in the process.
"If there is no exchange of power then it's not leathersex"
-- Joseph Bean, Leathersex