They are extremely important in biological reactions.
Enzymes lower the activation energy barrier and, therefore, allow the biological reactions to occur.
In this case the rate of the reaction is increased 800-fold. One can see that the effects of specificity of enzyme-substrate binding can greatly lower the activation energy and increase the rate of reaction dramatically. If one designed a substrate with one additional H-bond, the new substrate has approximately 1000x higher affinity for the enzyme and can bind and block the former substrate at low concentration. Michaelis Mentin kinetics are widely used because they correlate very well with experimental observations. At very low concentrations, this quantity is time independent.