Depending on the tool you are working with, you require oiled or non-oiled compressed air. Kindly keep in mind that it is important to regularly oil rotating tools and tools with impact mechanisms - follow the operating instructions. Ideally, use a mist oiler, which constantly discharges a fine oil mist into the compressed air.
On the other hand, other tools, such as paint spray guns or tyre inflating devices require oil-free compressed air. Special filters should be used for this. Details can be found in the operating instructions of your compressed air tool or in DIN ISO 8573-1.