Question

importance of knowing reaction rates​

Answer 1

Scaling up reactions for the plant - chem engineers often do that, in industry. that's the practical answer. Also, you can calculate the rate constant, which can be compared under different conditions to quantify the effect on rate from things like catalyst, solvent, heat, reactant ratio, etc.

Theoretically, you use rate laws to help elucidate reaction mechanisms or rate constants to simulate reactions by computer modeling.