Oil can be used for a great number of things, from frying and sauteing to making a salad dressing. However, one thing to be mindful of when heating is the oil’s smoke point.
If you raise an oil’s temperature past its smoke point, it will start to chemically break down and release smoke. Not only does this smoke taste terrible, it can release flammable gasses, something you do not want to happen next to an open flame.
Refined oils are put through a large refinement process wherein any and all imperfections are removed. These imperfections can lower an oil’s smoke point, which is why most refined oils have a much higher smoke point. However, many of these “impurities” can provide much of the flavour in the oil.
Thus, in general you want to use refined oils with a high smoke point when you are deep frying, sauteing or using high heat with the oil. If you are not heating the oils, in a salad dressing for example, it would be best to use an unrefined oil.
Fix.com provides an awesome overview of the smoke point of oil and the characteristics of various oils.
Source: Fix.com Blog