Here is , in my opinion, a good example of why I use a binder in my sausages. This is some Kabanosy I pulled from the smoker tonight.
I course ground the pork fat and fine ground the pork while stuffing in sheep casings. I started my smoker at 125*f and ramped up 15*f every hour until I hit a smoker temp of185*f . I then let my Kabanosy finish at 158*f, internal temp.
With out a binder, I could not have raised my smoker to 185* without experiencing some fat-out. In the photo you can see the fat still intact with a good bind.
I know I don't have to have an internal temp that high(per fsic log reduction tables) but I do like the texture of the sausage when finished at that temp.