The problem often with this is you do not really know what will be relevant or not in the future. That is why in Sonke Ahrens recommended in his book on the zettelkasten that you just input everything you find interesting into the zettelkasten. You may end up taking notes and never using them because your studies or professional life takes you in a completely different direction than you think.
The more you work with a set of information, the more trivial it will feel. That is just because the information is getting internalized in your human memory system. But it still can be useful because the act of inputting and connecting the information into a zettelkasten is a form of elaboration. Elaboration itself is considered a great learning technique, as it forces you to truly understand what you are reading.
I’d also add that this well trodden information may serve useful because it can serve as an anchor point to connect disparate pieces of information to, perhaps helping you see a hidden relationship between concepts in the future.
This is my somewhat related post I found in my notes