First of all I have to say, if you use a binder or not and you are happy with the sausage you make, that is what is important. I've made sausage without binders at times like most folks. That was to see what difference it made. Well it made a lot of difference. I have posted pics on here before of some of the stuff I have made. All of that sausage was made with added powdered dry milk. In my opinion [and I have said it before a few times LOL] to have a nice and juicy sausage [links] you should use a binder. To have that nice texture in summer sausage, you should use a binder. After all when all is said and done, the appearance is a important factor, to the taste buds before you even chomp on sausage.
What does a binder do as far as appearance? It prevents shrinkage!!. A binder does what the word says. It binds the fat to the meat, thus keeping the sausage nice and juicy. Just like making any sausage, when using a binder, the correct amount of water [or beer] should be used. After all the spices, cure [if used], binder and water have been mixed well, the end result should be a sticky mix ready for stuffing.
Well what about shrinkage. I can tell you that after smoking or cooking in the oven even 25 pounds of polish for example, I may have about two or three drops on the foil below the sausage or drip pan total. And that has been consistent with me so far. I use a binder in fresh sausage as well. I vary the amount of powdered milk I use depending on how lean of a type of sausage mix I have. The more fat in the mix I can go up to 1 cup per 5 pounds and less of course in something like summer sausage, but it's in there.
I remember my grandfather who owned a butcher shop in Germany. He would use bread crumbs in sausage to act as a binder. Well that was many years ago but the idea was the same. I have a buddy that uses the powdered milk in his burger for patties and meat loaf. Haven't tried that but I think I'll give it a shot.
So the main two reasons I use the binder is for appearance , less shrinkage, and a nice juicy end product. Reinhard