If an unsuitable of low quality engine oil is used then the reliability of the engine cannot be ensured. Wear inside the engine will increase unnecessarily during cold start, heavy load and high temperature operations (such as high performance engines).
The chosen oil should always correspond to the manufacturer's recommended specifications. If the oil is lacking in key properties then there is an increased risk of greater wear on the engine as well as premature failure of engine components.
Key properties of engine oil consist of (but not limited to):