When cooking a large piece of ribs or brisket do you cook all at once and prepare the rest for later or cook?!

If you like leftovers, then go ahead and cook the whole piece of meat at one time. Just wrap and freeze the rest for another time.
If you don't like leftovers, then only cook what you think you'll need.

Personally, I like leftovers. I usually cook extra and then freeze the rest in serving size portions for meals later on. Nothing says you have to eat it the next day. Sometimes I'll have the leftovers a week or a month later.

I would cook the whole thing at the same time. Then you will have leftovers. You can actually eat them in a day or two, they don't have to be consumed the next day. There are so many options when you have any leftover beef. Sandwiches, enchiladas, soup, stir-fry, chopped up on a salad or mixed with some mayo for a dip or topper for the salad.