From Energy.gov:
“A home energy audit, also known as a home energy assessment, is the first step to assess how much energy your home consumes and to evaluate what measures you can take to make your home more energy efficient. An assessment will show you problems that may, when corrected, save you significant amounts of money over time. […] A home energy checkup helps owners determine where their house is losing energy and money – and how such problems can be corrected to make the home more energy efficient. A professional technician — often called an energy auditor — can give your home a checkup”

As you might guess from your utilities bill, your HVAC can consume quite a bit of energy to keep your property warm, cool or circulating air as needed and, after a while, even the best systems can start to lose their efficiency. An Energy Audit can be very useful and recommended before the season changes to Winter or Summer.

See more on this at https://www.energy.gov/public-services/homes/home-weatherization/home-energy-audits.