The KISS Principle (Keep It Simple, Stupid) is self-descriptive and recognizes two things:
1. People (including product and service users) generally want things that are simple, meaning easy to learn and use.
2. A company that makes products or furnishes services may find simplicity an advantage for the company as well, since it tends to shorten time and reduce cost. (Where the company is trying to use the principle on behalf of users, however, design time may take longer and cost more, but the net effect will be beneficial since easy-to-learn-and-use products and services tend to be cheaper to produce and service in the long run.)
The New Hacker's Dictionary, edited by Eric Raymond, says that the KISS Principle is sometimes cited on a development project to fend off feature creep.
The somewhat related idea of Ockham's razor is about always looking for the simplest explanation.