You probably don't "need" it especially at well travelled spots, but I carry it every time because like most people mentioned it's a cheap, catch-all for bears and mountain lions. We hike with our three younger kids. In 10 years of living in CO, I haven't seen either mountain lions or bears on a trail, but I sure as hell have seen both at our house, repeatedly. We keep a few canisters of bear spray in the kitchen and in a storage box on the deck just in case, and so why not just clip one on my hiking pack? It takes two seconds, and it gives me some peace of mind if we are somewhere remote. I think of the same way I think of other gear in my pack. Here is a list of things I have never "needed": a first-aid kit, emergency blankets & ponchos, compass, knife, firestarter, whistle, flashlight. But I sure as hell have all of these things, even on shorter hikes (< 4 miles) because that's statistically when most people run into trouble. They are simply unprepared. My experience living and hiking in CO is that shit turns on a dime and like most insurance policies you don't need it until you really need it. And it's like $40 dollars.