Really annoying / pointless / never works.
Taxis drive around all the time. They don't have a selection of taxis that are kept especially for bookings, that just wait until they receive an advanced order.
Not including airport runs etc., but when people do it when you're going out - they never ever turn up at the time you want them to. Always about 20 minutes early or late.
Really had to get this off my chest. Can we stop doing it? Thanks.