My family had one when I was teen, a few years after being reassigned to new congregation. We didn't need one but they said they wanted to make sure they visited every family every year. They never opened, or pulled out, the bible but only asked us (my mom and her teen and college-aged kids) a bunch of personal questions...until my non-JW dad (who was listening to the whole thing from another room) walked in and asked the purpose of the visit.
They responded with something about "encouraging the flock" as they begin to put on their coats. That was the only shepherding call I've ever had.