i used to wear one all the time with a shovel and food in it. i hate it though (wearing it in the park and stuff, not the pack itself - arcteryx M20; id recommend the M30 for sure). now i only wear it if i absolutely have too, like when doing bc or have a camera, even with a camera though, i leave it with a lifty a lot so that i can have some fun runs too. basically essential if you're doing out of bounds; please take a probe, shovel and beacon... be good with them. if youre just doing in bounds bc, it depends if you want to just build a booter and sesh it all day, or just hit big lines i guess, and if you're willing to head down for lunch at the chalet or whatever.
spark notes: id avoid it wherever possible, but if you have stuff you need to carry (probe, shovel, food, camera), i think the answer is kinda obvious.