I always press it cos you never know when some nobhead will come round the corner speeding whilst updating his fb status, splatter me across the road which would then be my fault for not pressing it.
They also only tend to put crossings where there is too much traffic so stopping them for peds may just make em think walking thats an idea.
Non of which matters in practice though because the wait times are set so long (by the car people who manage this stuff) that by the time the green man appears I’ve made a dash for it .
In fact in many situations crossing actually reduce peds priority as traffic turning onto a road should give way to someone crossing anyway, they dont off course and dont have to once you install a crossing.