[sewercake]

As another reply mentioned, it seems like hand-written notes are good because the limitations on writing speed force you to synthesize information as it is relayed to you.

Outside of mathematical lectures, I find writing notes in something like notepad++ more fruitful. I can attempt mirror the structure of the speakers' argument using tabs/indentations, and quickly reformat the document as the logical structure becomes clearer.

[ghaff]

I've known people who liked using mindmaps for this purpose. Personally, I could never get into them but big fans exist.