I don't for general hacking/schooling/jumping but I do for fun rides and XC of course. However if i was jumping a horse i didn't know too well I would wear one
Only for XC but never for anything else nor does anyone I ride with and they are a variety of ages. Did a show cross event at weekend and you SJ in your XC kit as straight out of jumping arena onto xc course. Very odd to SJ in BP and not something i liked doing particularly but if i had to you just get used to it.