I think taking notes while reading fiction would be relatively unusual (outside fields like literary criticism), but taking notes while reading non-fiction is quite common, especially when grappling with denser material.
For example, I kept extensive notes while reading Bertrand Russell's History of Western Philosophy. The work assumes you're internalising as you go along, which is somewhat inescapable given the nature of the material. The author can't stop to re-explain some finer point of Aristotle's every time it is engaged with in the subsequent two thousand years.
Pausing to take notes helps one reflect on the material and solidify their understanding, but also gives them a quick reference later if necessary. I just use my phone's Notes app, to keep the barrier as low as possible.
For example, I kept extensive notes while reading Bertrand Russell's History of Western Philosophy. The work assumes you're internalising as you go along, which is somewhat inescapable given the nature of the material. The author can't stop to re-explain some finer point of Aristotle's every time it is engaged with in the subsequent two thousand years.
Pausing to take notes helps one reflect on the material and solidify their understanding, but also gives them a quick reference later if necessary. I just use my phone's Notes app, to keep the barrier as low as possible.