Failing to plug holes in the house left by the cable TV and air conditioning installers. Pet food left out over night. Monthly Sprays can usually be reduced or eliminated. Most pest control companies still base their cash flow on monthly services. Technicians of these companies are trained to spray, not to solve pest problems.
Most pesticides are repellent to the insects.
They will avoid the sprayed areas and go to other parts of a building. The above factors apply especially to many of the products the consumer buys and applies at home. This practice can have several adverse results. You will increase the smells and off gassing. You can stain or damage surfaces you spray.