One reason I have (and do) leave txp off is doing aerobatics under busy airspace - No intention of busting, but I'm of the belief that a signal heading up at a great rate of knots directly underneath the big tin might cause a few issues; despite the fact that there's no way I've got enought energy to get there - plus I'm moving sufficiently erratically I'd consider the signal to be just 'noise'. Otherwise, it's firmly on.
But that is completely the wrong attitude.
If you left the txpdr on, squwarking 7004 or whatever the aero's code is, then at least if I am flying in the general area I can a) see you on the traffic screen and b) if talking to ATC they can advise me "of someone doing aerobatics in your 12 o'clock".
ATC can advise other traffic of "an aeroplane doing aerobatics below controlled airspace" and hence there is no issue. Turning it off seems completely daft to me.