if things are going to get busy.
Its a bit of a diversion, but with the exception of low viz or thunderstorm activity within the TMA, it is pretty unusual for things to get sufficiently busy for a serious slot delay to be incurred at typical light GA levels.
I have suffered more slot delays since flying heavier higher stuff than I ever have flying unpressurised piston.
Of course, attempting to fly through the Clacton sector at 1600 on a Friday afternoon is asking for trouble
2D