First priority, I want my RD clients to be able to read my timing points descriptions and find them without difficulty in the light of day. I try to get them to do this in advance of race day. Paint marks can wear away quickly in high-traffic areas. I want them to not rely on paint marks.
I agree with you, Bob, about landmarks. In my experience, for as many RDs and course layout folks who do not have a sense of compass directions, there are two who wouldn't know a sycamore from kudzu. Yet, I know successful races have been conducted on courses you have measured and documented with this kind of notation.
I tried this for one race on the C&O Canal (hard-packed dirt & gravel) Towpath. The organizers were lost with what I thought were clear descriptions, i.e."2 feet north of double-trunk oak adjacent to dark stones on retaining wall". So, I went back with a camera and took pictures of each timing point from 4 compass points and put them all in a Word document with full descriptive captions. The RD had color copies of this produced at some expense. She said this was the only way they could lay out the course properly...