Regrettably I never obtained a PPL, having come into ATC via a route other than "cadetship". I am not convinced that holding a PPL or even having experience of flying light aircraft is of much benefit to someone working at one of the larger airports although it might well be almost essential for those controllers employed at training establishments (EGTK, etc)..
As a Heathrow controller I believe that I learned much more from the single ride I had on a BA 747 simulator about 20 years ago and the odd visit "up front" when I have flown on holiday.
I'm told that our emergency training sessions at LATCC are now attended by a pilot, which I suspect is of huge benefit to us (I'll find out on Friday!).