Usually that wasn't necessary since you could find some productive tasks for them (base camp chores, low risk areas, etc). I think we snagged a few members in this manner, as well.
Don't discount working at base camp. On the typical operation which lasts less than twelve hours or so, base camp is pretty minimal. But if the operation endures, base camp activity expands and becomes increasingly critical.
Concerned friends and relatives of the missing persons are often valuable in another regard. They can provide insight into habits and tendencies of the lost persons. This can be crucial in shaping the search effort.
You soon learn to be discreet in your comments in and around BC, and on the radio, because you never know who is present….
They also appreciate being near the communications center of the search so they can get up to date info on progress. Sometimes this convinces them to stay at base camp rather than be out where they may not learn of news about their loved ones right away.