The need for abstraction is not confined to Computer Science, or Computer Engineering. Let's consider, for example, a boat. Each component of a boat can be specified at an abstract level in which a great deal of detail is hidden. For example, in a boat (equipped with auxiliary power) the concept of an alternator is an abstraction. In essence an alternator converts mechanical energy into electrical energy. This is the most abstract specification. However for practical purposes a more detailed specification is required, which states what the mechanical and electrical interfaces are.
The mechanical interface
Likewise
The performance penalty incurred in using a given interface can be seen if we consider the V-belt drive. This is an easy mechanical interface to meet, but the efficiency and torque-transmission capabilities are small compared with (say) a gear transmission.