As a trainee with a PPL, i'm not sure it has helped me as much as I thought it would. Training to be an ATCO wll probably improve my flying more than I imagined possible, however.
The reason I don't think it was of much use (from an ATCO training point of view) is that i managed to obtain a PPL without ever talking to a ATC tower (always A/G or the odd FISO), without ever filing a flight plan, without receiving anything more than a FIS. So when I started training I had no cockpit experience of GMC, or even Air Control really. The only CAS I had ever been in was Solent CTA, and that was a rarity.
I've never flown in bad weather (unless you count rain showers) either. The PPL meant that I was already comfortable with broadcasting my voice, and with a lot of the basic phraseology, but I don't think that was a big problem for others anyway.
I enjoy flying immensely, don't get me wrong. I'm sure that flying training specifically targeted at ATCO familiarisation would be beneficial, I just don't think the training I did put me in any better position than my peers.
Ginger