I've ridden 1,000's of kms with flip-flops, wouldn't really recommend it safety-wise but never had a major incident. Once was hopping off a curb & flip-flop slipped & I hit the top-tube a bit. I think clipping adds a bit of safety but overall depends more on rider, bike, shoes/pedals, road surface etc. & of course clips have their own safety issues when stopping. I like clips mostly for the efficiency of using more muscles, esp for climbing. Clips help rider to hop over bumps easier but OTOH trials riders don't clip, right? BTW I read that BMX trend is to clips.