You may want to have a look at the recent posts
- Supernotes or Obsidian?
- How to use tags to categorize notes?
- Official introduction?
- How are you using hierarchies vs. tags?
where related topics are actively discussed.
Generally speaking, parents are a good way to provide context for an individual piece of information, and those contexts are not necessarily unique, which is why the multi-parent approach is so powerful.
Personally, I follow a paradigm that is based on a concept-based hierarchy, i.e. I use concepts like Algebra or Health as the building block of my central hierarchy tree and add non-concept information such as assertions and relations as that tree’s leaves. And yes, I use PARA as the root of that tree.