According to the US Department of Energy (energy.gov), drafts from poor insulation can result in up to a 10-20% loss of energy (heat in winter, cool air in summer). For the average homeowner, this could cost as much as $2000 per year in lost energy costs.
Insulation has a big impact on how well your HVAC unit will keep up with the demands of your household. Insulation works largely by reducing heat loss through conduction (heat loss through materials) but also by preventing loss through convection (think drafts).
Proper insulation can affect your HVAC system in several ways.
In short, investing in insulation can save you on energy costs, improve comfort, and put less strain on your HVAC system, increasing its lifespan and resulting in less wear and repairs over time.