In practice, I find it to be dramatically better than previous notebook environments for data analysis, exploratory programming / computational research, prototyping, data visualization, and writing/reading interactive documents (blog posts, software library documentation, expository papers ...). It has a lower barrier to starting new projects, a lower-friction flow throughout
I find it better at every stage of my thinking process from blank page up through final code/document, and would recommend it vs. Jupyter or Matlab or Mathematica in every case unless some specific software library is needed which is unavailable in Javascript. The only other tool I really need is pen and paper, though I also use http://desmos.com/calculator and Photoshop a fair bit.
In practice I think taking care not to accidentally shadow variables is much more important: this dependency business only makes sense once you have a clear idea of what you need and by that point you are mostly done anyway.
[1] https://jupyter-contrib-nbextensions.readthedocs.io/en/lates...