I would think it depends on the type of relationship you have and if you have an STD. I don't have an STD, neither does my husband. We're in a totally monogamous relationship, so there isn't a worry about either of us suddenly getting one either. In a committed relationship like ours, I don't see a need for one, but if you're relationship is open, you're engaging in sex with multiple people, or know that the person has an STD, than I would suggest using one.