Brad Isaacs writes at Lifehacker that as long as you keep notes, you can avoid a lot of problems with communication and expectations. For example, taking notes on your boss’ requests helps you “prove” your understanding of the request to them, when they expect something different a week later.
But notes are no more reliable than human memories, from the point of view of other people. There’s two issues: people record their mistaken beliefs (sometimes they just plain lie in their notes), and people forge notes.
Sure, you can accurately record that “On Monday 11 a.m., Wendy asked for a green TPS report to be finished by Wednesday at 3 p.m.”
However, so many things can go wrong. In one scenario, Wendy asked for a red TPS report, and you wrote it down wrong. In another scenario, Wendy needs the report by Tuesday; you deliberately wrote down Wednesday so that you can take your time. In another scenario, Wendy never asked for any report; you just wrote it down (on Thursday) to make it look like you did lots of work this week.
Having said that, notes can be really useful when appropriate. In my line of work, we take notes on our our work and our clients. Since our stakeholders are happy to assume that our computer systems are reliable, our notes are taken to have been written in accordance with the time stamp. Notes also help the organisation to give evidence, even when the individual who wrote the notes has moved on. In any case, the courts will only believe the notes to the extent that they trust the individuals who wrote them, and the organisation that produced them as “evidence”.
So yeah, notes are great for reminding yourself of things. But all they prove to other people is that you like to take notes. Even then it’s not conclusive proof.