Choose portability over efficiency. The example given here is of the Atari 2600 which was the first successful home video game. Most of the code for the game cartridges was very efficient but nonportable. The author proposes that Atari would have been the largest supplier of software in the world if its code had been portable. A sub-tenet of the leverage tenet is allow other people to use your code to leverage their own work.
Many programmers hoard their source code.
Unix source code was originally fairly inexpensive compared to the cost of developing a new operating system, and companies started choosing Unix as the platform to build their software on. Companies who chose Unix spent their effort and money on developing their applications, rather than on maintaining and developing an operating system. I'd strongly recommend this book for people from all operating system environments.