Why do lurchers & sighthounds wear large leather collars?

Some of the dogs I see in the park have these broad collars, about 2-3 inches wide on.

What are they for, and do I need one for Bungle?

Linda says:

I phone Pip!

But when the dog is at home, I take the large collar off to prevent the dog from getting sore, or developing bald patches round its neck.

Pip says:

Lurchers and Greys wear these special collars for support of their neck and throat (if the dog was pulling on the lead, and a narrow collar is used, the dogs neck can be damaged). The wide part of the collar should be under the throat to give full support when the dog is on the lead.

Kerri says:

Also, an ordinary collar can sometimes be shaken loose. These 'fishtail' collars can help prevent that from happening too.