I thought at first that I was the odd one out reading this topic.
Personally, I love to draw really anywhere. In private, sure it's great for concentration. But when you're in public, you have to be outside of your normal comfort zone, and it often helps you meet like-minded people.
Currently I don't have a nice place to draw (being in the city) but if I'm ever near a park, I sit and just start drawing. If there's anything around me that interests me, I try to get it down as quickly as possible.
Another thing though that you just can't get from working in private in a break in immersion. Sometimes, especially when working on something creatively, we're so sucked into our worlds that we can't see the obvious mistakes. Being in the zone for too long can make us blind to our own works. Being in public not only helps with pulling us out from time to time, it could also lead to direct opinions that, while not usually the business of random passer's-by, could be an early taste of online opinions.
Of course, there is a sort of courtesy that should be given to someone who is focused on art. Obviously if someone comes up to you and says, "wow that's awesome!" but then asks, "can I see more?" That can be very rude, especially if the artist is still in the middle of their... anything, but sometimes it can be very welcomed.