The User-Agent field is a great way to detect a polite robot (and even, if it supports robots.txt, to ask it to avoid certain pages). So this header field is a

The User-Agent field is a great way to detect a polite robot (and even, if it supports robots.txt, to ask it to avoid certain pages). So this header field is a useful signal for analytics. It's not at all trustworthy, but in practice it's useful.