It's only dead space if you are not using it. I like to open my laptop and place it on the tray. When the person in front reclines, I am forced to sit still for the duration of the flight. I usually fly from Europe to Asia, so 10-12 hours.
To be fair, I have actually once seen someone not recline, but they had four or five visits from cabin crew before the lights went off making sure they were okay, or if they wanted to be moved, or if there was a fault with their seat. Like, even the crew thought it was an unusual occurrence.
Yet every thread that touches on this on HN, there are people saying "I never recline, what about the person behind me?". And then they complain about being uncomfortable!