The feature is incredibly convenient if you happen to be chatting with someone in person and want to add him as a Facebook friend. Rather than tapping out his name and wasting minutes scrolling through a list of similarly named individuals, you can just ask your new pal to open up the Find Friends Nearby page and add him with a quick tap.
Opening up the Find My Friends page, while convenient, also exposes you to potential awkward or creepy moments. There is always a chance that someone you are avoiding or not interested in interacting with will happen to have the same page open — and spot your name. He or she would instantly know that you are nearby and quickly view the public information on your Facebook profile.