I almost never let my dogs stay outside when no-one is home. That isn't to say I think it is irresponsible for people to do it that way…I am just not comfortable with it.
A few instances in our yard, that have solidified my thinking...
-we have had a tree fall thru our fence (last fall)
-we have had a dog who never EVER dug at all, dig a hole under the fence and trot around to the front (last week)
-we have had construction workers remove a panel of the fence (they were allowed to, of course, but it was easy to do)
-we have had dogs fight over fresh kills in the yard...ugh....
-we have had a dog slip into shock from *something...we don't know what...bug bite, allergy...whatever, had someone not been there to take her to the vet, she probably would have died
-we have had one dog (same as above) pull a tarp off of a pile of a woodpile (we thought it was out of reach), get her head stuck in the one small hole in it, and be trapped for a few minutes until we could get to her. I also worry that an incident like that could cause a massive fight/attack.
So that is just in the last few years, in our safe, country yard....
It isn't worth the risk to me. But lately, I have been considering the possibility of kennel runs outside, with a small cool/warm building...that seems like a good compromise between inside crate and complete freedom in the yard.