The whole point of the Captain sending an email to the relief crew, advising the intended rest for the flight,
is so you can plan to be rested for your stint in the seat.
You are missing his point, yosemite.
I think subwoofer was bringing attention to the fact that inflight relief is meant so that
the whole crew should be rested and alert while at the controls, as opposed to just the two guys in the seat being rested for takeoff and landing (which is how many of our crew interpret in-flight rest requirements).
I definitely agree, an e-mail when planning on doing something non-standard should be a minimum. This also helps if the whole crew is based in the same location. I always thank the Captain for such a courtesy, it certainly makes life easier and it certainly shows good leadership and CRM, which is quite lacking among many at Cathay.
If you are planning on doing what is expected, then an email is not as important but still appreciated.
I forgot where I read it, but I remember some article about noise complaints. It said that people where a lot more understanding when they knew about the noise and how long it would last, than when they where caught by surprise and had no information as to the duration. A little off topic, but somehow I see how this could also apply to other unknown variables, such as rest.