You never know when you may need help yourself, so I always ask if I see someone with a mechanical if they need assistance. I think it all balances out anyway as I've needed help myself more times than I would like but that is the nature of the sport. Anything can & will happen no matter how prepared you are. In fact that is how I met my best friend. On this one ride from hell a number of years ago, I had a front flat & was on the outskirt of town middle of nowhere. Changed it & continued on but flatted again on the front after only a few hundred yards. Changed it again with my last tube & the same thing happened again. Tried calling home for a ride from friends & family but no one was picking up & it was starting to get dark. I was SOL with no more tubes & so I started walking. This guy flies by in a sports car & stops. Asks if I need help & I explained my situation & he offered to drive me home. Turns out he's also a fellow cyclist & we've been friends ever since.