Lint can build-up over time on the lint filter which reduces air flow within the dryer. This causes longer drying time. Clothes may not dry in just a single cycle, thus, there is a tendency of overworking the dryer which can cause damage to the machine.
Furthermore, build-up of lint on the filter is a fire hazard. It can cause the dryer to overheat. Since lint is known to be highly flammable, even just a small spark inside the dryer can easily ignite the lint causing fire.
To avoid unnecessary repairs and possible fire in your home, be sure to clean your lint filter and dryer regularly.