Or perhaps, just hiding them from normal users. I muck with the source. Categories are a way of dividing code into functional areas on a small scale. In normal code development, I worry only about categories. Packages are a way of storing code into a repository.
Parcels are the deployed version of a package.
At deployment time, one wouldn't have the repository. So, during development I normally work only with the system browser and the Package browser. I only use the 'Global' browser namespace view when I am defining or redefining a namespace. These divisions are useful. In the hands of an expert like yourself they are extremely powerful.