Did I eat late before bed? Higher BP overnight. Drink any alcohol at all after, say, 12pm? Higher BP overnight. So it's still useful and interesting to see the overnight values change and shift around.
However, the contrarian in my mind says that it's not smart to ONLY pay attention to your deep rest state BP, since that only applies to a fraction of the day. And if you're running around at high values for the rest of the day, you're still potentially doing damage to your kidneys, retinas, etc - the sensitive blood vessel stuff.
So it's a useful device, it's useful to have the data, but it's also still a bit of black box.
The fact that 80% of all high blood pressure is of unknown physiological cause is a real head scratcher considering that cardiac misadventures are the leading cause of death in the Western world.