Why is a figure-8 placed on the BH bridge?

A pre-installed throw line is a unique concept- even simple. Say a lead climber makes a high climb so he can work him/herself down for what ever purpose- be it work or play. If climbing with others- which is always advisable for high climbs-it would be easy for the lead climber to set a high throw line that gives access to his position without panic response time from below. Nothing high tech here. It would require that someone be trained in fundemental rescue technique but the time to set a high rope would be shortened significantly. GOOD IDEA!