as far as TX nothing needs to be controlled at any event, no transmitter needs to be impounded IF the people used the frequency pins like they should and didn't just flip on their radios for the heck of it at the most inopportune time, unfortunately that just doesn't always happen so CDs choose to do TX impound, this controls how many TX are in the hands of the pilots at any given time and when the right people are doing it (people who actually have a bit of common sense) there are no chances of two TX being out of impound that are on the same freq so you can't be shot down by an 'Oh, I'm sorry, I just wanted to cycle my retracts'.

also at most events they try to keep the number of pilots in the air to a maximum of 5 at the time, without some sort of control you'd find a dozen or so people out there and one hell of a traffic jam in the pattern.

TX impound is just adding one more person to the loop to check that no two people are on the same freq and to me it's a good thing, while there are allot of people out there i trust not to turn on their radio without the pin, some people do (and some do it often), i was just shot down a few weeks ago by someone who just wanted to check his throws after hooking up and putting his wing on, it was just sunday flying so no impound, but if his TX was in an impound they wouldn't of let it out because i had the pin so that would of saved the incident. with 2.4 the likelihood of interference is drastically reduced but no reason why you can't goto the impound and check out a 2.4 pin and return it at the end of the day. you'll still have your TX in hand all day, but you're still in the habit of getting the pin.

kc
EDIT: Gary, the quote was in reference to the comments about impounds that had given out the wrong freq pin, it's careless mistakes like that, that often lead to mishaps at events, same for people who have different freqs for different planes and they have the pin for plane #1 but swap to #2 without getting a new pin. no system works perfect, but with responsible people running the impound the chances are reduced for shooting down someone, especially for the not so responsible pilots who hate impound and frequency control in the first place.