Personal notes, a team wiki and a knowledge base for AI differ in who reads them: your future self, your colleagues, a model. All three have to answer what to keep, how to organize it, how it gets found and who maintains it. Research on personal collections finds that most 'finding' is re-finding things you have already seen; research on enterprise wikis finds that once the person who tidied or wrote the content leaves, it starts to decay.
Before choosing a note tool, ask five things: can other programs open its files, do links survive renaming, can you search and filter, does it sync across devices, and does it work offline. Obsidian's notes are just Markdown files in a folder on your computer, but syntax such as block references can't be followed outside Obsidian, and on iPhone only two sync methods are officially recommended. Notion's databases are powerful, but an export takes only one view, callouts become HTML, and an export can't simply be uploaded back to restore your workspace. Before switching tools, export once and open the result in another program.
For files people create themselves, research keeps finding that most retrieval happens by clicking through folders, and better search tools haven't changed that much; few people use tags, and those who do mostly apply just one. So notes are worth organizing, but each note needs only one main home, the structure shouldn't get too deep, and folders shouldn't get too full. PARA sorts things by how close they are to your current work, Johnny.Decimal allows at most ten per level and fixes each item's place with a number; the numbers in both are their authors' experience, not experimental findings.
To decide whether to keep something, ask three questions in order: can I name a concrete use for it, can I find it again later, can I write one sentence of my own about it. No use, don't keep it; if the original is findable again keep only a link, otherwise save a copy; only items with that sentence go into the knowledge base, the rest go on a to-read list. Empty the inbox every week. The reason behind it: every keep-or-skip decision risks two errors, keeping too much buries what matters and keeping too little means searching again, and loosening or tightening your threshold only trades one error for the other.