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.