[makecheck]

Even if it were "much faster", this isn't really the goal, because code writing is usually the quickest step; at least, it is if your employees are competent. What matters more is how maintainable your project is, and how easy it is to deploy.

I may use several libraries, but I lean heavily on platforms; for instance, I have no problem using what's in /usr/lib from a typical Linux distribution, or the Python standard library. This keeps deployment pretty simple, and I can rely on well-tested components that are widely used and unlikely to go away. The platform libraries are also usually free. And I can ask or hire anyone who knows something about them.

While I don't rule out incorporating another library, this is definitely not a rule of programming. A 3rd party library has to do a lot to justify its added deployment complexity. After all, maintainers will have to read through API documentation just to figure out what something does, and this shouldn't take more time than it would take to read through my own implementation of the functions.