Another danger for non-breakaway collars is the cat getting it's jaw caught in it. This happend to one of our cats when I was a kid and it was awful. Luckily, the cat eventually came to us with the issue so that we could cut it off him, but he was stuck that way (jaw stretched open - unable to eat or drink) for at least 12 hours and possibly longer. I felt so bad for him!

We tried putting a collar on our last cat and he wouldn't have any of it. It was always off him in 5 minutes and always when we weren't looking. We don't even bother with our new cat even though he's indoor/outdoor. We have only two neighbors in close proximity (within a couple of miles) and they both know our cat, so it's not really a big deal. If we lived near the city, he'd be an indoor cat. He is microchipped, of course.