I went to a Cat rehoming place at the weekend with some friends. It made me really want to step up with regard looking into keeping a pet.
There's no way I could ever visit a cats/dogs home - I'd want to take the whole lot of them home!
On the question of leaving a pet (especially a dog) on their own all day, I think they
can get used to it, but you wouldn't want to do it with a puppy. My brother "adopted" my sister's Springer, who'd been treated fairly badly to be honest, so he was used to being left alone. He was fine being left in the house during the day (with the radio for company!), so long as he got plenty of walks and attention in the morning and evening.
When that dog died, he (my brother that is) got a Springer puppy, who needed a lot more attention! Fortunately he was able to go home from work at lunchtimes to quickly visit the dog, but not everyone can do that of course. I don't think it's an ideal situation.
Personally, although I love cats and dogs, I wouldn't get one because I am out for 11 hours a day and there's no-one else who could help out with walks/feeding etc. Maybe when I retire (or get made redundant...)