I use it for two purposes:

1. Useful practical information or checklists on disease topics (I'm a physician). Sometimes they are reminders, or useful knowledge that is generally gleaned from experience / colleagues. Things that can be hard to google.

2. Notes on general business stuff - i.e. "called such and such agency and Wendy said I need to speak to other person next Monday on tel xxxx". Or dates my car needs servicing, or who I'm insured with.

At the moment I use vimwiki, and it works well.