I wouldn’t call it necessary, but you’d be surprised how often a knife comes in handy once you start carrying one. The vast majority of the time you’re just gonna use it to clean your nails or open boxes or some such. But for those every once in a while things its much nicer to have a knife sitting in my pocket than to find myself searching or wishing for a way to cut or pry something. Like that one time when my shoe laces got tangled in my bike chain and I ended up sitting bruised in the gutter of a rural road trying to untangle myself for 20+ minutes. Eventually a neighbor spotted me and brought out some scissors.
I also do a bit of fishing, boating, camping, hiking etc. And a lot of cooking at other peoples houses, in my experience other people have shitty kitchen knives so it can useful to have one decent one on hand. So I have specific reasons for carrying it other than avoiding the occasional inconvenience or accident.
