It might help you document possession d'état, i.e. the fact that your grandfather continued to make use of his citizenship. Beyond that the rules are complex and it's difficult to determine whether you are a French citizen or not with so little information.
Do note however that the main obstacle to having your French citizenship recognized is the fact that French citizenship effectively lapses for people born abroad whose French parents have lived abroad for more than 50 years without making use of their citizenship. Since 1970 is almost 50 years ago, it's probably advisable to look into this swiftly.
Importantly, as explained in the comments, your grand-father's citizenship isn't terribly relevant. Your parents' citizenship is what matters. If one of them was French when you were born, continued to use their French citizenship and you can prove all that, then you are French yourself. If they did not, your grand-father's citizenship is not enough and you first need one of your parents to establish their citizenship before you can do anything.
Either way, when applying for a “certificat de nationalité française”, you only need to submit documentation regarding your parents' citizenship and prove that you are indeed their child. You would not typically go back to your grand-parents.