I know people get worked up about it but I can’t see the issue really other than “I found this spot first”. People in the middle of the moor are usually familiar with both, and respectful enough to re-hide both caches and LBs when found.
One of my caches actually shares a hide with a letterbox now, I had to find a better place for it in the vicinity and it was the only hide available. I wouldn’t have shared if the hide wasn’t huge, in the middle of nowhere and totally obvious in the first place (piled stones in front of big overhang)!
I get a lot of logs saying why they’re in the same place and I guess I will have to archive it when I visit them next, but it does seem a shame, a lot of people myself included enjoy finding a letterbox as much as a cache, and surely a letterbox is meant to be found by those who are looking!
For some reason letterboxes go missing a lot (unlike geocaches which are easier to find, go figure), so giving hints to locations openly would be a huge issue. Nice topic!