Begging is having the submissive plead with the dominant to receive something. It is most often used for the submissive to plead for pleasure, orgasm, or a pleasure scene. Used to gain release, it can also be a method of reminding the submissive that their body is no longer their own, and even the physical pleasure of pain or orgasm must be granted by the dominant.  

Begging, can be a means of exerting control or power over the submissive. By making the submissive beg for things, it is a powerful reminder that the submissive is no longer free to make their own choices without, at the very least, permission of the dominant. This can bring to the forefront the emotional response of the power exchange. In this way, it is basically used as one of many things to keep the power exchange in the forefront of the participants minds. 

Begging can also be used by dominant during a punishment. They can request or order the submissive to first thank the dominant for each strike and ask for another. In this way, begging is a way of bringing home the reasons for the punishment, and the fact that the consequences are indeed a punishment. For many submissives, having to do this keeps their minds from relaxing into sub space and turning the pain of corporal punishment into pleasure. It acheives this by forcing the submissive to particpate actively in their own punishment, therefor giving the mind something it has to concentrate on. It can keep the submissive focused during a punishment, by centering their focus on what is happening to them, and with each plea re-inforcing the fact that misbehavior has consequences. 

The physical act of begging can be a sexual turn on for people. Seeing the submissive in an obviously submissive pose, pleading with the dominant,  can cause significant sexual arousal in both parties. Kneeling is the most common submissive pose, and just seeing a person in that position can arouse a dominant. However, one need not be kneeling to beg. Positioning for begging is up to the dominant, and some prefer certain positions for certain situations. 

Begging can take many forms. From a simple "Please Master/Mistress, may I speak freely?" to a long process of repeated entreaties while in a particular position, using specific language and tones of voice. For example, a submissive on their knees, naked, legs spread, arms folded behind their back, head up, eyes lowered, with a soft tone of voice begs their master/mistress for permission to orgasm. The entreaty itself could go something like this "Please, Master, may your slut cum for you?" or "Please Master/Mistress, may I cum now? Please Master/Mistress?" Such an entreaty can include body motions designed to show the master/mistress all parts of the body that they own, as well as the state of physical arousal. 

Some dominants prefer that when their submissive's beg, they include statements of who is in charge or devotion and submission. How one begs is really up to the dominant, and the dominant should make it clear to the submissive what they prefer in what situation.  

Begging contains an inherent humiliation factor for the submissive. This humiliation can be a great turn on for some people. The humiliation factor can be increased in intensity by requiring "vulgar" language during begging. In this manner, the humiliation factor can be used as a means of teaching the submissive humility if the submissive seems to be overly proud or arrogant. Though, any acts which include overt humiliation, must be handled carefully and with much forethought to ensure they are being done in as safe a manner as possible for the submissive's mental well being. Teaching humility is one thing, destroying self esteem is something else entirely. 

Begging is also often used as a part of role play scenes. I've seen it most often when people describe scenes in which one partner plays the role of a "child" and begs their "daddy" or "mommy" to spank them, or let them have a privalege they are wanting. In this way, begging increases the realism of the role play scene and makes it more satisfying for those involved by putting the submissive in a more "child-like" mindset.  

Begging, as one can see, is another aspect of BDSM which is very varied in it's uses, turn ons, and meanings. It is a personal choice whether or not to include begging in the relationship.