Manufacturers expect customers to maintain their appliance well. They recommend annual servicing to ensure the furnace or air conditioner is cleaned and small issues are fixed. This reduces the load on main components and reduces wear.
However, if the annual maintenance isn’t performed, the components of the main unit are more likely to sustain damage and wear easily. This will make manufacturers reluctant to grant warranty benefits to you.
Also note that it is a good idea to schedule annual maintenance with a reliable and approved service provider, ideally the same company that installed it. This is especially important because the labour portion of the warranty from the local HVAC contractor who sold you your unit, will often only be covered if you have them perform annual maintenance, particularly for extended labour warranties of 2 – 10 years.
If you’re consistent with maintenance, the unit will last for a long time and you won’t have to pay for most of the replacements.