Our university physics teacher allowed us to bring one-page self-made cheat sheet. By the time you compressed the essence of a whole course into a one-pager, you were pretty much done learning. :))
My own experience of making up those cheat sheets is the same as yours, the effort put in to create them is an excellent teaching tool in itself, as you're studying and distilling all the stuff you don't know well, and by the time you're done, you hardly have to refer to it in the exam anyway.
For physics, they'd just give us a page with all the formulas but with no context aside from the letters in them, so if you knew roughly what it should look like, you could find it and you're not at so much risk of making a basic error under pressure.
This raised eyebrows of the TA's proctoring the exam, but like, if you don't know the stuff, a page isn't going to help you at that point.