You really shouldn't spend much time on writing stuff down. If you have a really quick mnemonic or two for something you always forget, maybe, but nothing that takes a significant amount of time. If you know it well enough to remember to write it on the sheet, you can probably pull up that bit of information when needed anyway.
What I used the sheet for was just for a few notes on particular questions - like if there was a question I couldn't figure out and might come back to I would write down the number and a short (very short) description of what my difficulty was, if simply highlighting/greying out answers wasn't going to give enough information when I came back to it.