Now that is a question, isn't it? There is no wrong or right answer but there is a clear and focused way to figure out if you are someone would desire a safeword or not. They can be an important part of the play or something that is never used, but provides the security that some people need. BDSM play can be risky, does bring about the potential for uncomfortable situations, raises physical limitations or triggers mental or emotional walls to come crashing down. In any of these instances, it would be very helpful to have a way to alert the dominant. It's a verbal security blanket.
What is a safeword?
A safeword is a word or signal that ends BDSM play instantly. It can be any word that isn't a part of common play speech, so selecting 'Stop,' is usually discouraged as people tend to use stop playfully and the confusion could cause unneeded halting of a perfectly good scene. The most common safeword is the Stoplight system. 'Red' meaning stop, 'Yellow' for slow down, or a physical discomfort alarm and 'Green' means all is a go. Other safewords I have seen used are the submissive's full name, random words like, 'bananas', dropping keys and a subtle hand system that may not work in low lit situations.
Do you need a safeword?
That all depends. I would recommend that if you have never played with this person before that you have one. Other situations that would warrant guarding a safeword would be new play activities, extremely risky play and anything in a public play space.
There are people who do not use safewords for one reason or another. I'm not here to discredit them or say that having a safeword is the only way to play, but it is a safer way for new experiences. I can assume that later on in my relationship that a safeword would become obsolete as my Master and I are very intuitive of each other and we know the responses for the other during play. He can read me like a book most of the time and feel very safe with him.
Negotiating a scene
When playing with someone you don't know or are only casually seeing, it is important to negotiate the scene every single time and make sure that the safeword is known for both parties. This will prevent severe misunderstandings later on. Part of negotiation should always be about safety; from physical limitations, triggers and hard limits. If your play is at a public location, make sure that if there is a space-wide safeword, you know what it is.
When to use the safeword
A safeword is a last resort. It shouldn't be used lightly for any occasion as the consequences of playing with the safeword could be the 'Cry Wolf' syndrome. You call your safeword too many times in jest then you may find yourself without a play partner pretty quickly. No one wants to play with someone that doesn't take safety and established protocol seriously.
Whether you decide to have a safeword or not is a personal decision. For me, it was a no brainer, however, coming up with the word I wanted wasn't. I finally settled on the stoplight system and haven't had to use to use it often. It's almost a badge of play, to say that your safeword is dusty :P
What is your safeword? Do you have it documented in your training resume yet?