We can talk meaningfully about these different roles for notes. Which is the point of this thread.
After we note that the point of notes is really, "have information at the GM's fingertips", sure. The top level of this is like, "What is the point of a word processor?" Given that an argument over frelling railroading came up within two pages, I felt that cementing the general was important. Notes are not "to impose a railroad" or similar style war stuff.
A more useful form of the question may be - "As a GM, how do you structure or use notes during a session of play to enhance the play experience?"
This may separate between notes the GM is holding behind their screen at runtime from, say, notes back in their setting binder that they use during adventure design.
We probably also need to come to agreement on what qualifies as "notes". In basic form, notes are "a brief record of facts, topics, or thoughts, written down as an aid to memory." A detailed map of London would not count as notes in my book. A quickly scrawled diagram of London's overall districts might.
With those couple of things mentioned, then...
When using published adventure content, I rarely need much in the way of notes. I may pull out stats on monsters or the like, because they are rarely included in a way that's easy to reference in play. But otherwise, I find the text of the adventure sufficient for my needs.
When doing my own adventure design, notes are a whole other ballgame. I don't generally do a full adventure writeup - everything is notes. I wind up with two levels - one (typically kept in MS OneNote these days) for idea generation and organization, the other, used at runtime, is abstracted from the first, sometimes with stats for things added.
Then, the notes for doing D&D (which, for a dungeon crawl, is going to be a sketched map and bits about encounters) is vastly different from when I run Ashen Stars (which is more about the series of events that the characters are investiagting, and the information bits that can be found, and how.