Air filtration is an extremely important part of spray painting and should not be overlooked. You risk hours of work and hundreds of dollars of materials being wasted. Oil in paint can cause many defects but the most common and immediate is fish eyes which usually will result in requiring a re paint, further down the track the oil and water will try to escape from underneath the paint causing it to bubble which is commonly referred to as humidity blisters. Because an air compressor sucks in a high amount of air from the environment it will also take the moisture and oil with it so before you breathe or spray with it I recommend using multiple filters and even a breathable air quality check before using an air fed respirator or you may be breathing in cancerous and toxic gasses.