While cis women might wear their vibrators proudly on their sleeves, many straight cis men would be horrified at the thought of telling their friends that they (gasp) use a sex toy, that doesn't mean they can't be enjoyed by everyone!
So yeah...erections. Whether you have a penis or your partner does (or both!), the strength and endurance of an erection can be kind of a sticking point. Cock rings can both help you get a stronger erection and maintain that erection for longer.