In addition to what rak1507 said, knowing what parts you’re composing gives you a more intimate feel for how the pieces fit together. Knowing that you’re build

In addition to what rak1507 said, knowing what parts you’re composing gives you a more intimate feel for how the pieces fit together. Knowing that you’re building on top of a handful of functions you probably already have some intuition for is quite different from using a library function and simply trusting that the authors have done their due diligence.