In our school groin protection is not mandatory but it is suggested. When I first started training I would only use a groin cup when I entered a tournament (it was mandatory). But two things changed that. First was my instructor needed a dummy and I volunteered. When he did the technique, the groin strike was with full impact. My knees slammed together and I dropped to the floor. All he said was "see, it works". And than he reminded me that I had the option of wearing one and that choosing not to wear one would be cheating myself and my training partners. My training partners would not be able to practice the technique without trying not to hurt me. The second thing was sparring practice. I was sparring with one of my instuctors and he threw a quick lead kick to my groin. Guess what? Cup broke and I didn't know until I felt a pinch...and guess what was pinched, starts with a "t". I just imagined if i hadn't been wearing a cup I would've been crushed, if you know what I mean.
Just for the record, a friend of mine has just been diagnosed with some kind of cancer. I'm not sure what kind it is, but they had to remove this tumor right above his groin area. The doctor said that more than likely, it was from being hit in the groin area a long time ago.
And in our school, when we train it is common to ask anyone male or female if they are wearing a groin cup. When we do self defense, if they aren't wearing a cup, we let tthem feel a charlie horse in their inner thigh, if we're sparring, we don't hold back...they end up getting a cup real soon.