So, Andrew has NO idea where he heard this tip. And several permutations of the cursory google search yield no results on why this is a good tip. But we think it’s a good tip, so here you go.
Use the edge of a quarter (or any coin for that matter) to make markings on walls when measuring, identifying nail holes needing filling, etc. We discovered that a coin marks very faintly yet well enough to see and you can quickly rub it off with your finger without too many smudges. This is perfect for someone like me who is less than stellar at getting measurements right the first time and needs to remark when hanging pictures, etc.
Below, a visual of the faint marking made by the quarter identifying a nail hole to fill: