The first thing to say about power in BDSM is that it needs to be exercised and experienced to be effective. This may sound obvious, but because BDSM is frequently about power of one sort or another between two people, if the partner with the power doesn't use it then their partner can't experience it and be effected by it. Consequently, when power is unused there is no BDSM.
There are many different types of power which can appear in BDSM relationships or activities. Beyond mere strength, power can also lie in a skill or in a special ability because these can be things used to effect you and your partner. Frequently, one of the main forms of power is the need or desire to engage your partner. When put into play, this can create an intense engagement. This is often the driver which shapes the relationship or which determines which psychological activities or physical activities are explored.
Other forms of power, beyond need or desire, are used in the actual engagement, and these can include:
- Physical strength, coordination, size, or speed,
- Mental ability - knowledge, IQ, quick wittedness, mental robustness, or empathy,
- Experience and practice with BDSM feelings and reactions from yourself and from a partner,
- Skill with ropes, floggers, or other BDSM equipment, and
- Sexual technique.
It is the intensity of need or desire, combined with using the different forms of power listed above which makes manifest BDSM.
Disparity of power
BDSM has to do with one person having more power or control than the other, and using it. This is particularly the case in dominance and submission and humiliation, but also occurs in physical activities ranging from cutting and piercing, through bondage and sensory deprivation.
Usually, some aspect of enacting this disparity of power is the key to feelings of satisfaction. In other words, if the disparity of power isn't utilised, then there's no positive BDSM effect.
In the case of bondage, we can see the disparity of power in the person-being-tied having their movement restricted at the "whim" of their partner. Some forms of bondage play involve the partner-in-control drawing attention to, or teasing, their tied partner about how helpless they are and how dependent they are on their partner for ability to go to the toilet, get a drink, and so on.
When power is lacking
BDSM is seen by many to be physical. But when there are other needs involved beyond what can be satisfied in a purely physical way, technically perfect execution of, say, a flogging scene or an interrogation can be completely unsatisfying.
It is often the case that a physical scene is an opportunity, or a context, in which other aspects of BDSM---such as power---can be expressed without the physical side necessarily being an end in itself. It may well be that without the power aspect being exercised, the physical scene itself might just as well not have been done.
In this sense, there can be some similarity with the idea of pain in BDSM. Pain is not an end, but is a means through which other satisfactions can be found.