The purpose of tuning is to get your arrows (or bare shafts) to fly straight and true, without wobbles. This involves:
1. Brace height
2. Nock point
3. Arrow spine
4. Arrow length
5. Proper fit of arrow nocks
6. Point or broadhead weight
7. In some cases, tail weight
As Scott mentioned, this tuning configuration is for a particular bow configuration, and if you change your bowstring, draw length, string grip (split to 3 under), bow quiver, shelf pads, or string silencers, you might need to re-tune your arrows again.