What does it mean that orphan nodes need connection or removal?

An idea connected to nothing else is either missing links or not worth keeping.

Example: You open your note vault and find 47 notes with zero incoming or outgoing links. Some are fragments from a conference two years ago. Some are half-formed ideas you never developed. A few are genuinely important concepts you simply forgot to connect. Until you triage them — linking the valuable ones and deleting the rest — they contribute nothing to your thinking. They are cognitive dead weight: consuming attention during searches without producing insight.

Try this: Open your knowledge system — Obsidian, Notion, a folder of text files, whatever you use. Find every note with zero links in either direction. Sort them into three piles: (1) connect — the idea is valuable and you can link it to at least two existing notes right now, (2) incubate — the idea might matter but you cannot connect it yet, so tag it with a review date, (3) delete — the idea has decayed past usefulness. Execute all three actions in one session. Count the results.