Coming back to this after more thought I think that maybe this is more important to the mistress than to the sub. It happened that the best mistresses I sessioned with did not use it, and others did. I think that having a safe word gives peace of mind to some mistresses. Those who don't use it don't need it, because they are better at reading your reactions. As a general rule those who did not use it knew better than me how hard they could push me, while those who relied on my feedback where more likely to do too little or too much.

There is also the possibility that I was just lucky.