The air filter is an important part of the vehicle's intake system. It allows the engine to breathe without the threat of contamination. An engine needs a precise mixture of fuel and air in order to run efficiently air enters the system through the air filter, which catches the dirt and other foreign particles, preventing them from entering the system and possibly damaging your engine. Changing your filters on a regular basis can have a significant impact on the engine life and performance.
Check your owner's manual for the manufacturer's recommended intervals. But depending upon where and how you drive, a good rule of thumb is every 12 months or 12,000 miles. As air filters get clogged with dirt, grime, and debris, the volume of air is restricted, decreasing performance and engine power.
If ignored long enough, a contaminated air filter can cause your engine to work harder negatively impacting both efficiency and economy. There's little safety risk, just decreased power and performance, but neglecting your air filter can have a big impact on the environment.