When I first got Bus, I crated him and Annie in separate crates beside each other when I was gone, as I didn't trust either as far as housebreaking at that point, and even play at that point could go south if someone got too rough or got their feelings hurt. After about a year, I set up an expen (with wire top, and linoleum underneath in case they peed) and would leave them both in there. Eventually Annie got to where she was peeing every time I left them (either beside their beds so they would be drenched, or along the bottom of the pen so it wicked along the whole edge :< - massive cleanup every day- she's always been a "dirty" dog), so I took it down and relegated them back to individual crates, as I didn't want to crate them together because I was afraid they might have a tussle in the smaller space, and it wasn't fair for Bus to be trapped with Annie peeing on their blanket/beds. Annie didn't take well to going back to the crate, so I avoid it whenever possible, I don't even have one set up for them at my house right now, because I never leave Annie there, and if I leave Bus, I just gate him in one room. They can be out at my house for short times, but I make sure I have any toys/food/bones put up because Bus does resource guard over high value items like that and Annie likes to creep around him and push his buttons. They are fine if there are no "prizes" out, and when I leave both at my moms', they stay out together. When I take them to work with me, I usually kennel them together, but seperate for feeding/toys/treats.
APBTs are my other favorite breed, and I've had a dog who could never be left with another dog because she would pick a fight as soon as the "police" were away (she couldn't be with some of them even supervised). On the other hand, my first was totally cold with our smaller house dogs (would run away if they went after her- but was very dog aggressive to strange/larger dogs), and we left her alone with them for short periods regularly. She usually went into my room and slept on my bed when we were gone, and there was a gate that they couldn't get over easily, so she had her own space. We also had a cocker, and a Chi mix, who were shut in the kitchen with Annie anytime we left for longer periods, and would all 3 pile into the cocker's crate to sleep (door open, other crates available).
When I have another APBT, it will be separated from Bus (and my cats) when I'm not around, just to be safe. I've seen the results of a lot of bad household dog fights when owners aren't home (often at least 1 dog seriously injured or dead), and while it can happen with any breed, more often than not the one causing most of the damage is a pit or pit mix- frequently a dog who has never had any issues with dog aggression. One of my co-workers got a an Ambully/pit looking dog last year (was a foster and she kept her- prior to this dog she wasn't really a fan of the breed), sweet dog, and from what I've seen, fine with other dogs, but I cringe every time I see that she's kenneled that dog and her elderly cocker together at my workplace- overnight with no one there.