It's often better for pedestrians when there's a button. Because the light usually changes pretty quickly after pressing the button. Otherwise you'd have to wait until the timer switches the lights.
It's usually used for pedestrian crossings where pedestrians are rather rare.
Sometimes people stand at intersections and just chat and don't want to cross. And in Germany and Hungary where I used such buttons, they are definitely not placebo, because the switch comes quickly and when you forget to press it it does not switch.
It's usually used for pedestrian crossings where pedestrians are rather rare.