Some sites are not meaningfully-structured by their URL "path". This generally isn't good for a variety of reasons (such as SEO), but nonetheless we often have to analyze sites that aren't ideal as we are working to improve them. If sites are not meaningfully structured by the URL, then it may be necessary to slice the site by content type or to derive the site sections by some other means.
Note that lower level fields may sometimes be needed to compute more useful fields. Also, sometimes the higher level fields may be more difficult to compute, so they are not always worth it.
This is totally built in and automatic in Chimera.