I have seen some collars used that looked way too tight and others way to loose for it's purpose. I know the purpose of one is to help hold the saddle in place and more useful if you are even in competition with cattle or using speed events.
I have found it useful even with the saddle become a little loose during a trail ride.
However, at one time I think I got the darn collar too tight and it rubbed a spot on the horse's shoulders and more in the center of the chest. So I have been letting it out more loose.
So what is the proper way to set a collar and how to test it?