I should also say that not all events have changing tents - they tend to be confined to longer distance races where space in transition can be at a premium and with perhaps more than a 1000 taking part, then bloody messy and unworkable if kit was at racking spots!
bags work as follows
3 bags - bike, run, street
rock up with bike and run bags with kit you need for each leg, deposit street clothes in street bag, hang all 3 bags on racking spot corresponding with race number and toodle off to the swim with swim kit.
out of swim, grab bike bag and put bike kit on and put swim kit in this bag - deposit bag - it will be rehung for you.
off bike, grab run bag, put run kit on, put bike kit in bag and deposit as above.
finish event and grab all 3 bags from haning spot, change into street clothes - go get pissed 
some events only provide bike and run bags so you have to work out something else for street kit - friend, family etc.
Edited: 06/03/2013 at 14:57