probably to aid flushing out thw system if the equipment has been outside, as it could be a bit quicker than taking the carby apart....
Truth be told, if its sat long enough to have water in there most of the time it needs a full clean anyway, I use the drain on my scott bonnar to drain the stale fuel out if its been sitting a while and I forget to run it dry on its previous use, bit it takes all of 30 seconds to remove the bowl andd tip it out anyway.
Some of the newer tecumsehs even have them and they also leak, I guess in america where the tecumseh version of the kirby may be used on a snowblower or something it may come in handy if it managed to ingest some water into the fuel while you were on the run.
