I don't leave collars on my dogs. They only wear them when out. However,whilst looking for poodle pictures I came across this page which shows what can happen if collars are too tight (and the dog is clearly neglected). I have had this happen in a neighbours cat who's collar was so tight that her neck was raw and I doubt if her ex-owners would have said they were neglecting her they just didnt check her collar as she grew.
http://hometown.aol.com/petpalsgc/PetPalsInc.html
warning it isn't very nice and I'm amazed the dog survived!

My dogs also never wear there collars indoors and only have them on when out on there walks.

Karen

same here :D

Important point, I agree! I always keep collars on(dogs!) all the time, after escaping puppy incidents, returned only due to wearing a collar! but always check that I can get two fingers comfortably under them, but that they're not too loose, so can't easily catch on anything .
Emily

Bec

That site had the most awful examples of neglect and abuse - I am gobsmacked how people can let that happen and do that to any living thing.

Pam n the boys - who only wear their collars when out with me - they are secure otherwise and have the most remote chance of getting out.