I agree, there is no need to hang off like a monkey while riding around on the street (assuming one doesn't ride like an ...... on the street). Personally, I don't ride like an idiot on public roads. I just ride around and enjoy being on a bike. I save my asshattery for the track. On the street, I don't hang off the bike. I might move over and inch or so, and drop my upper body a little bit, if I do some riding through the mountains that is a little quicker than my "going to the store" pace, but I don't hang off anywhere near like I do on the track. I don't drag knees and elbows and .... on the street.
But with that being said, you will not find a single racer anywhere in the country (or world for that matter) that is racing at a top-5 Club level Expert pace and above, that sits in the middle of the seat and doesn't hang off the bike.
Lean angle is finite, when you run out of it, you crash. Good BP reduces the lean angle for any given speed+radius, that fact cannot be argued. That newfound lean angle can either be left in reserve as a safety margin, or utilized to go faster.
We all have seen the pictures of guys racing 15-20-25 years ago all crossed up with the "Doohan style" BP. They made the most of what they had as far as knowledge and understanding of the physics, the tires, bikes, suspension, etc. However, that would not work today. It would be impossible to carry modern competitive corner speeds with that crossed up BP.
A few years ago even Rossi admitted that he could no longer be competitive with guys like Marquez and Lorenzo unless he worked on his BP. He couldn't match their entry, mid-corner, and exit speeds because at any given time he had to carry more lean angle. So he spent the offseason revamping his BP...and it worked. He immediately started battling for wins and podiums much more consistently.