A knowledge management system (AKA personal knowledge management system or PKM) can be used both to outsource mental storage of knowledge AND organise and strengthen thinking itself.
The human brain operates with The Forgetting Curve, meaning it is easy for knowledge to be lost.
Creating a record of knowledge increases the longevity of ideas for the user.
A knowledge management system seeks to make that collection of knowledge more useful to the user through making information more easily discoverable.
This could be through a search system or links for connecting content
A good PKM system is more than mere storage and retrieval.
It makes thinking easier by providing a Framework for thinking
The structure of the PKM system provides a structure for thinking itself.
It enables discovery of old ideas by Resurfacing notes
It allows old ideas to be developed overtime by growing notes through the system of Resurfacing notes
A digital, web-based system can be updated with the input of others (through Working with the door open).
Notion is particularly valuable in this. How to Build a Second Brain in Notion, by Maria Aldrey explores this idea in detail, though I feel I have built a better, more personal system for myself in the , and other personal areas of the workspace.