There is an old saying when it comes to parts cleaning: “Like dissolves like”.
This comes from the world of chemistry, and is really quite a simple and useful phrase to remember. In chemistry molecules are described as being polar or non-polar. (Think north and south pole on the Earth) Polar molecules have a polarity that causes them to attract other molecules that have polarity, while non-polar molecules do not.
Water is a polar molecule. Oil is not. At the molecular level this is why “oil and water don’t mix”. Chemically they are dissimilar and cannot absorb each others molecules. By contrast salt IS polar; this is why you can dissolve salt in water.
Solvent based cleaning systems (like Vapor Degreasers) are used when you need to clean true oils from your manufactured parts. Aqueous Cleaning Systems are used to clean water based materials from your parts.