I run almost daily with my aussie and she's off leash then, but yeah I have to be on the lookout that we don't encounter other dogs. I trust mine a lot and she stays with me but you never know what the other might do, so there's that.
My sister-in-law has a 9-month old baby and that's what I'm most anxious about, he just started crawling, so now I never take our dog off leash when he's around; wouldn't be able to forgive myself if anything happened to him. Even though she's playful around him, she does make some unexpected movements, does not know her own power and impact and a dog is still a dog. Sister-in-law has a 10-year old toller retriever herself and she literally trusts him with the baby everywhere, even left alone. I don't get that but it's her own responsibility at least.