By onelittlekingdom:
Every submissive individual who enters into a D/s relationship should be given an agreed upon word, that will immediately stop any scene or moment within the dynamic, that the submissive can use any time they need things to stop, so they can talk with their Dominant about what is going on, as equals. There are several reasons that safewords are both essential, and important.
1. Safety - A safeword is what assures a submissive that they will not suffer abuse at the hands of their Dominant. Whether a sub has taken enough of a punishment, finds a new hard limit, or just needs a scene to stop so they can gather themselves for a few minutes, their safeword is the only thing that stands between their knowledge of their own needs, and whatever the will of their Dominant is in the moment. Since the only difference between much of what goes on in BDSM, and abuse, is a matter of consent, the safeword must exist to give the submissive the power to stop consent. In the absence of a safeword, the door is open for abuse to occur. Any Dominant that does not immediately stop and take stock of their submissive’s needs upon hearing their safeword, should be feared and abandoned. Any Dominant who does not offer their submissive the power of a safeword within their relationship should likewise be feared and abandoned.
Communication - Many submissives enjoy challenging their Dominant. It can be confusing for a Dominant to know how serious a submissive is being about things they express, while they are being challenging, without a safeword in place. A safeword therefore gives a Dominant the peace of mind of knowing that they are not going too far with their submissive, and allows them the luxury of being able to conduct a scene, or moment within a relationship freely, and without hesitation or guesswork in reference to their submissive.
Respect - Offering their submissive a last vestige of their former power, before submission was given, is a declaration of respect for the submissive by their Dominant. It is a promise that abuse will not occur, a declaration that their submission is prized enough to not be treated in an offhand way, and an acknowledgement that the submissive deserves to have a voice in the relationship, regardless of the length of that relationship.
Please Note: Many D/s couples will boast the lack of a safeword within their relationship, citing its absence as evidence of absolute trust of the Dominant within the relationship. However, it should be remembered that any individual can be seen as entirely trustworthy until such time that they break your trust. The lack of a safeword opens the door to abuse, is an exercise in bad communication, and creates an imbalance of power that is required within BDSM. As soon as you give your submission to a Dominant, the first order of business should be an agreed upon safeword within the relationship.