I think safewords are a must in the getting-to-know-you phase ( it's a clear expression of the trust needed in such encounters) but, as has been mentioned above, partners who know each other well can perceive when things need to slow down or pause so safewords aren't as necessary then. I'm giggling a little at the idea of a woman over my lap stammering the word "pinapple" while I spank her!
Rafa