This is Amola. She is a Sheltie. 

For: I love dogs. I've almost always had two dogs around. A friend for Diddy, who is extremely social, almost to a fault. 

I can't go anywhere now anyway because I wouldn't kennel Diddy. If I ever HAD to go somewhere I'd ask a friend to stay over. 

Against: I don't have a yard. So they have to be walked, likely at the same time. Two dogs who think with their noses could yank me in half. 

If I ever have to move, it's hard enough to find a place that takes one dog, let alone two. 

Diddy didn't destroy anything and was trustworthy out of his crate after just TWO days. I can't possibly be that fortunate again. 

Diddy is a barker when I leave. He quiets down, and maybe another dog would keep him calm in the first place. The opposite could happen though. I could have TWO barkers when I leave, and for who knows how long.