We are newbies. This is what my wife's Dom has said on the topic of "safe words"

A personal view on "safewords" and unilateral vetos - You will always have the option of calling a stop at any time during a meeting but I am not myself a fan of things like safe words, for two reasons. Firstly, they imply that a Dom does not know when enough is too much. If done well there should be an implicit understanding in a meeting of when to push and when to do the opposite - hence my frequent communication during a meeting. Secondly, if armed with a safeword the temptation for the Sub is to use it too early. The impact of this is that it can sometimes get in the way of a very necessary element - that of pushing oneself and testing limits. For example, before I spanked you the first time, would you have ever thought that a spanking could bring such pleasurable feelings? That what started as a stong might turn into such heat and erotic sensation? Sometimes we need to experiment and suspend judgement and reflect/review afterwards. So you will always have the option to say "stop now" and this will happen immediately, but my expectation is that we may never need this.

Your thoughts and advice gratefully received.