Some prefer that sort of anonymity. I personally find it holds too many variables for comfort. You don't know if the guy is a psychopath. or has some sort of STD or worse. You don't want to take him home with you for that reason, so you have to get a hotel room or make some other arrangements. As you don't have a relationship with him, it likely will be a one-time thing, and you may find yourself repeatedly searching for a new prospect, with the aforementioned risks each time, multiplying your chances that something or things will go wrong.
I've shared my wife with two of my friends over the years. One relationship lasted about 15 years--the other a little over 30. It has worked well for everyone involved. But to each, his own. If you prefer strangers, I'm sure you have your reasons.