I never have a collar on my dog unless I am working that dog. Lots of dogs wear collars 24/7.
I absolutely never have a collar on any dog that is playing with or spending time with other dogs. A tooth can get caught in a collar and strangle the dog when the stuck dog panics. The stuck dog can end up with a broken tooth or jaw.
And I'm just the opposite. My dogs wear their collars pretty much 24/7.
After Ilka got her teeth caught in Leo's collar while they were playing (and yes, it was a pretty terrifying situation), I would take Leo's collar off right before we went outside, and put it back on as soon as we came inside.
Needless to say, a slip (choke) collar or a prong collar should NEVER be left on a dog, but should be removed immediately after a training session is done.
It's mostly up to you. There have been incidences where dog's collars have been caught on something and they've ended up panicking and strangling themselves when no one is supervising them or available to help unstick them, which is a possibility at night when everyone is sleeping.
Personally, I take my dog's collar off when he's in the house or in his crate. In the house is mostly because the jingling of the tags kind of irritates me, haha. Crate is because the tags can get stuck in the bars, and then the dog panics and strangles themselves. I always put the collar on when we go for walks or he's outside in case something happens and he gets loose.
I keep tags on at all times, terrified my dogs will go walkies on their own and it's much easier for a good Samaritan to read a phone number off a tag than go to a vet and have the dog scanned. When they've gotten out they sit in the front yard and bark but in a panic who knows what could happen. Tags are on tag collars that are loose enough to slip over their heads. In the 15 years I've been doing this the worst thing that's happened is Ginger would come into the house with her paw through it. Tightened it up a bit and so far so good.
My dogs only wear collars when we leave our own property. They play rough and could easily get hooked on each other.
They ABSOLUTELY have their collars off when in their crates. Kane has escaped his crate more than once and I have no doubt if he had been wearing a collar it would have gotten caught and it would have been a very bad situation. He also actually did catch his collar tags on his crate once while I was right there and able to take his collar off immediately.
I'm not too concerned about them not having tags in case they escape. They're both tattooed and micro-chipped. Nobody would be able to get close enough to Kane to check his tags anyway.
My dogs are not runners so I don't keep their collar on as I don't want to take a risk (plus it really messes up the hair on long haired dogs). But if your dogs have a tendency to run out, it's probably worth leaving it on.
I always put collars on my dogs when we are travelling even though two of them are in crates. Otherwise they never wear collars unless I am training them. I know there is a bit of a risk when they are in crates but as they are quiet in the crates and just sleep the whole time, I always think of the fact if I was in a car accident and they ran off, there is more likelihood of them being returned. Some of them are micro chipped but not all of them.
I cannot imagine a need to keep the collar on at night. In general wrt collars, if the main concern is dog tags, be sure to have your dog microchipped. Also, when your dog DOES wear a collar, make it as loose as possible without the danger of the dog slipping out. Dogs with big heads can have quite loose collars and that is a bit safer and more comfortable.