Never - Once.

There's some crossing here which always go Green in a set order and I've got them memorized off by heart now so at those ones I don't even bother using the button as it makes no difference to when it goes Green. Others I'll press it once. I'll ram it a few times after a couple of minutes if I'm really impatient.

But it's just as fruitless as those drivers who think the closer they edge to the white line on the road, little by little, the faster the traffic light will go green.