Masters Of The Bare Bow, Vol. 2 Ken Beck demonstrates and explains perfectly, bare shaft tuning ......... with regard to understanding spine and choosing an arrow, this is an absolute must see for any archer I'd say.
Spine charts will get you marginally close if one where to just build arrows using a chart and hope for the best when you let your completed arrows fly .......which is nowhere near good enough for most. You have to bare shaft.
There may be times that you might want to shoot a particular broadhead and that head is way out of your normal weight range - example, the lightest head that an outfit offers is a 160 and you mainly shoot 125's. You can shoot that heavy head, but may have to go WAY out of what a spine charts tells ya, and your heavy broadhead won't even be noted on that chart. You'd have to do homework and best guess what shaft or adjustments to a shaft to make and then bare shaft test to confirm good flight.
You may notice that a shaft that shows a bit stiff when shot bare, is brought right in to the money when the broadhead is finally mounted and balanced. Every individual shaft/arrow build intended to shoot at an animal that I put together, is spine checked, bare shaft tested, Is shot completed with broadhead at least a half dozen times and sometimes more, before it makes the quiver to hit the woods. I don't do a best first arrow up front thing......they all fly exactly the same and perfectly or they don't go hunting.