We've owned Corgi's for what seems like forever and one of the first things we were told was not to leave the collar on the dog when they are not leaded. The reasoning was that because of their short legs they ran the risk of getting tangled and stuck on stuff with the possibility of death.
We have collars and tags but we only use them when camping or travelling. Other than that we use the harness, no tags, when we walk them.
The reason I ask this question is because I see photos on this site with unleaded Corgis wearing collars with tags.
I've had fun reading all these replies as all of the points of view have merit and show that it is difficult to make a decision on merit alone! I am a believer on following one's personal comfort level when it comes to self and the care of our children or animals, because often what works for one person does not work for another and vice-versa. I would not leave dogs alone who are collared and interact in play, unless they had breakaway collars.
That said, for many years I ran a community lost and found and many dogs got lost who never were supposed to get out. Accidental stuff happens and we cannot foresee every eventuality. Having also done a lot of rescue work and brought home many a stray and gotten stuck with my share of them, I no longer take home any dog that does not have a collar and tags. Yes, they may be microchipped, but by the time I take a dog home, take it to the vet to be scanned and find out he is NOT microchipped, I'm still stuck with the dog because I could not put him out at that point. That's just me... Microchips work well if a dog is taken to a shelter, or to prove a dog is yours. but do not incourage a stranger to take your dog in. Most well cared for dogs never get loose, a staggering number of dogs do get lost, and many of these are well cared for, not intentionally allowed to roam.
On the other hand, a small number of dogs are strangled by their collars (except for chokers which should never be left on any dog), but no one can predict where any individual dog will fall within those statistics, so find YOUR comfort level and go with that.