There are also cases, where it is convenient to carry over strict hierarchies already applied in practice. For example I use a namespace to model files of my local filesystem and wire them up within Logseq:
/home/home/daniel/home/daniel/applications
/usr/
etc.
Another thing is called “Enumeration” in programming. That is a strict, fix set of values, that shall belong together - for example a page Project status, with subpages Project status/Active, Project status/Finished. Namespaces have the advantage, that you can either search for references of particual values like Project status/Finished, or any value within Project status, as searching for namespace parents finds children as well. (If namespaces wouldn’t provide latter, you also could just use block references).
Another example for enums is a rating system r/+1, r/+2, r/+3 etc. and all ratings are grouped up by namespace r.
I currently like to use sidebar queries with a bit of CSS customization. Sidebar looks like this with Logseq as current page:
