A dominant may withhold something, such as sexual gratification or permission to use the toilet, to encourage the submissive to beg. This could be part of humiliation play or simply to reinforce the roles in a BDSM relationship. Begging also helps remind submissives that their bodies are no longer their own; they belong to the dominant.
A dominant may also use begging as a component of a punishment. For example, a submissive may be required to beg to be spanked. This forces the submissive to engage with his or her punishment, rather than trying to disassociate from it.
Begging can also be a powerful component of some role-playing scenarios, such as parent-child role-playing. Begging can add realism to these types of scenes which makes them more intense.