I have always used/heard the 6 foot rule: Place uncut fabric with folded edges together, step back 6 feet and see if they still go together. Place blocks on design wall and step back 6 feet to see if overall layout is to your liking, and finally, if you can't see a mistake at 6 feet, you are good to go (sorry, not in the galloping horse camp!).
You can substitute any measurement that works for you with the 6 feet.