Is the concept of a ual "safe word" between spouses actually detrimental to a relationship?

My wife and I are very pionate... and pain is the name of our game :-) I know i'm an ever loving sadist LOL and she loves every bit of it. We've been happily married for 4 years in our 20's and life is great. But i've recently thought of the idea of us developing a safe word if I ever take it "too far" (which I don't see) But i feel like if she had to use the word it would make me wary in the future to do certain things, and kind of derail our relationship even a slight bit but still it would make things different. Is that a valid concern?