My first teacher also did not encourage notes taking. My subsequent teacher did. The danger about note taking, in the form of keeping a diary of every single sitting, is that the imaginative mind will try to come up with new things every time, or the mind will try to value add to what actually happened. That said, there are also advantages to keeping notes.
For a period of time, I didn't have easy access to my teacher. I'd only see him once or twice a year when I made the trip to Thailand. Sometimes, the visions/disturbances/obstructions/hindrances would be hitting me fast and furiously. So, I started scribbling notes on pieces of paper. Later on, I compiled them into a little notebook. When I had the chance to visit my teacher, I'd go through the notebook with him and he'll strike off the unimportant ones and explain the important ones. Of coz, in the beginning, I'd write alot...and most of it is nonsense that my imaginative mind had value added in. Much later, I'd read back to what I wrote, and laugh at how my ego inflated so many points. The important thing is to keep it as a notebook. Meaning, don't analyze. If you see "a ball of light", just write "a ball of light" and don't write "a ball of light which I think is energy".
What I found useful about keeping a notebook is that writing it down stopped me from constantly thinking about it. The other thing is that sometimes another insight that comes up months or years later, is actually the answer to a previous question that I had jotted down.
In a nutshell, it's not for everyone, but I feel that if you wanna keep a notebook, you need to be very mindful, objective and discipline about it.
~ swimming upstream is tough work! ~