Systems are easier
to express and understand
Classes designed to fit the problem tend to express it better. This means that when you write the code, youre describing your solution in the terms of the problem space (Put the grommet in the bin) rather than the terms of the computer, which is the solution space (Set the bit in the chip that means that the relay will close). You deal with higher-level concepts and can do much more with a single line of code.
The other benefit of this ease of expression is maintenance, which (if reports can be believed) is a huge portion of the cost over a programs lifetime. If a program is easier to understand, then its easier to maintain. This can also reduce the cost of creating and maintaining the documentation.