Dying is a tricky business. Die young, and you never grow old or experience loss, but live long and you'll have to watch friends and family suffer. In many ways, being left behind is the worst, especially when the departed sends letters from the grave.
One dying mother in England left not notes but a wish list for her sons and husband. Eat together, be on time, make up after a fight, treat girlfriends with respect, and never smoke, ride a motorbike, or join the armed forces. It seems sweet, but potentially troubling.
I once heard (I think on This American Life) about a dying mother who wrote letters to her daughter that were to be delivered every birthday until her 30th. The letters became a source of annual upset that often weren't read until b-day celebrations died down. She wasn't sorry she had them, but she was relieved when they stopped.
I can understand a dying person would want to tell loved ones how to carry on, but is it more disturbing to the living than it's worth?