I definitely do not think it is necessary. I opened up to my senior manager during my internship a while about having a bit of a stutter at times, and asked for some tips when presenting meetings at work. He gave some interesting story about one of their colleagues having Tourette's syndrome and having to present to clients and all that, and he explained that a preface at times was extremely helpful and actually improved relationships at work. Totally different than stuttering, I know. But yeah, I do not think that it is necessary, and I would honestly only apply this to a work/professional setting when presenting to people you are familiar with or something, and not going to worry about being judged immensely. It just depends on you, I'm sure this would not work for some people. The couple times I did it, it was awesome and went well, and made me feel more ok with my stutter and build up confidence. It's all about how you word it, it's not warning people, it's more so opening up to them. Again, I am not doing this all the time to everybody, only in situations where I was familiar with the group I was presenting to, some already know I stutter. I also have this horrible stutter on my own name when asked what my name is. I found it useful to, instead of going literally insane worrying about how bad my stutter is going to be, to just let it happen (accept it I guess) and then afterward explain that sometimes I have this weird stutter tick on my name. One time somebody actually related and said he has this horrible stutter on the name of the company he works for!