The utility of a ritual

Many people adhere to the ritual according to which a phone conversation doesn't end until the parties all agree by saying their good-byes.

But some people just hang up when they are done and they think the other party is (or parties are) done.

You can hang up too soon that way, and miss information the (or an) other party would have passed on, or even attempted to pass on but was prevented by your sudden hangup.