I think starting out with such an easy build tool is a good idea, but I’d like to also stress the importance of understanding the underlying build system.
Although nwb is suitable for a lot of projects, it is not suitable for every kind of project yet. For example, if I want to do server prerendering, then I probably need to understand how to generate the prerendering bundle using raw webpack (+loaders) and Babel.
The best is to know both: Understanding both the underlying build system, and how the convenient tool works, allows me to monkey-patch the tool to fit my needs without having to resort back to setting things up manually. This saves me so much time compared to setting up the underlying tools manually.