Those star ratings are for the game situations "2nd and short" "3rd and long" etc.
If they are starred for the situation, they will pop up in coach suggestions. I assume the higher the star rating the more often/higher they'll pop up there. If you aren't using coach suggestions for picking play calls, then there is no reason to bother with those star ratings.
Even using an "empty playbook" some plays with have their base playbook star ratings. Every play you added would have no star rating unless you manually give them one. A base team playbook will have plays "starred" so you could call coach suggestions, which i think is a default on the game until you switch that play calling style.