Not really, as it all depends on the level of infestation you have. Even the best products tend to leave a few stray fleas behind. Adding an insect growth regulator ensures the eggs are rendered infertile. When this occurs, the strays that managed to evade the initial “blast” are unable to start a new colony with fleas that hatch from the eggs that were not killed. Of course, you do not need to use it every time. However, if the infestation has spread to other rooms, it is wise to use an insect growth regulator.