All of these are good reasons to leash - and of course, because it's the law.
I was jogging about a year ago, and mind you, I have never, EVER been afraid of dogs, EVER. However, I was jogging, and I could see an unleashed dog, without an owner in site ahead of me, and I crossed the street. I could see it was a pit bull (and we don't need to go into the whole pit bull argument, but, I will say, I just don't care for them) and the dog started to run after me. I slowed down, and the dog started barking and really coming after me. I completely panicked, and thankfully, I was next to my neighbor's house and started frantically knocking on their door. They didn't answer, but thank GOD their door was unlocked, because I just let myself in! Again, thankfully I KNOW these people, I had no other choice but to somehow get out of this dog's way! I'm guessing I would have been attacked had I not sought shelter.
NOW, I'm petrified of unleashed dogs. And living near the community center, there are often unleashed dogs running around in the field with their owners. Which is fine, but what really irks me, is when the dogs run up to me and my kids to say hi. I don't want to be afraid of dogs, but after that incident - I am, and REALLY do not appreciate dogs coming up to us unleashed. And it happens ALL the time. And the owners are always, "Oh, don't worry, they are friendly!" They might be, but try to remember that not all people are fond of dogs (although, I am really fond of dogs, but, again, frightened of dogs I don't know...) And we all know dogs can be unpredictable around kids, so, it's really not appropriate when unleashed dogs come running up to my kids - even though they might be the friendliest dog around - you just never, never know.