I leave a collar on my cat at all times. It is break-away and I test the fit and buckle regularly. I would not do the same with one that was not designed to break-away.

I also leave a collar on my dog at all times (except during bathing), but his collar is not a break-away style. However, I feel the risk is greater that he will get loose than it is that he will get his collar caught. That said, in multiple dog households, the risk can definitely change. I have personally heard more stories about dogs tangling up on each other's collars than I have about dogs becoming caught on inaminate objects. It probably depends on the play style of the dogs involved as well as the way the dog(s) react to stressful situations.

This is certainly a very important topic to consider! I hope that all of our PTers have made the investment to microchip all pets, whether or not they wear collars regularly.