Will the engine oil be damaged if the oil is not cleaned when changing the oil?

When we usually do maintenance and change the oil, the auto repair shop usually lifts the car with a lift to drain the old oil and change the new oil.

However, many car owners find that some oil will be left after each maintenance. What is going on? Did the auto repair shop drain the engine oil? How to use the remaining new engine oil? How can we make this extra engine oil play its value?