Jafo,
I had gotten my electric grinder primarily for making sausages. But found all sorts of uses for it. And it's much more efficient, I've found, than hand machines---which are what I grew up using. But either one does the job.
Anyway, you will, on rare occasion, have to add fat to the meat you are grinding. It really depends on what your main meat is, and the end purpose. As Cathy notes, venison (all game, in fact) benefits from the addition of some beef or pork fat. Most beef really doesn't (unless you're going with top cuts, such as sirloin for hamburgers).
I do not, btw, stock up on ground meat. For me it makes more sense to keep the big cuts in the freezer, and grind them as needed. But we don't do a lot of meatloafs and burgers, per se. So stocking ground meat doesn't make a lot of sense for us, because it wouldn't get used up fast enough.
Now then, as to physical grinding, there are several things to consider.
1. It's better to have the meats cold than not. I have no idea why this is so, but, pragmatically, it's true. Cold meats just grind better.
2. Your initial instinct will be to use the small plate. Don't do it! The small plate makes meat almost paste like; which is alright for forcemeat, but not for burgers, sausage, and the like. Use the medium plate. And don't double grind. In some cases, the large plate actually makes the most sense---try it for chili, for instance. But by and large it's a specialty tool, rarely used.
3. Trim away the connective tissue. Again, you'll initially think this isn't necessary because it all get ground up. But that's not true. Much of it will not grind, and merely clogs the machine. And the connective tissue can add off flavors to the meat.
4. Cut the meat into chuncks just big enough to fit in the hopper. Season the chunks as evenly as possible. Then grind the meat.