Setup is the process of setting the bow up correctly and making sure that everything is within tolerance and safe to shoot. This is vital for all archers.
Tuning is the process of taking a well set up bow and making it work well with the archer by making adapting it to be forgiving for the archer. The focus here is more on intermediate to expert archers, as the benefit may be reduced for a novice who still lacks consistency.
A bow will not make you shoot better. It will only be less likely to expose your flaws and incidental mistakes.