I think the answer is in your post – it all comes down to control. If you’re 100% certain that your dog will come when called, then let him off the lead. 99% isn’t good enough – after all, you wouldn’t drive a car whose brakes worked 99% of the time.

My own dog returns 100% of the time when he’s in the right mood, which depends on the prevailing rabbit conditions. He also doesn’t like other dogs charging at him albeit that their intentions are friendly, and once in a while will turn aggressive when he considers that he’s under attack. I can’t risk it, so I always keep him on a lead unless I’m absolutely certain that other dogs aren’t in sight.

Our daily walk takes us past an infants’ school with a notice outside stating pretty much what you said in your last sentence. Although I know Gizmo won’t jump up at children, they don’t, so I slip his lead on so that they feel safer.