I used to sleep 6 or less hours a night when I was younger, and I was chronically sleep deprived. I had this mentality that there weren't enough hours in the day, and there were so many things I wanted to do that it made no sense to waste another 2-3 hours just lying there. But as I got older (meaning, post-college), increased responsibilities and the need for complex thinking made this impossible. A year or two out of college, and any sort of sleep deprivation sapped my motivation, ability to focus, and ability to think strategically. When I haven't slept enough, all I can accomplish during a whole day is rote tasks. So now, I think of the 9 hours I try to sleep every night as an investment in the other 15 hours I'll have awake. Or to quantify it for you:

Option 1 - 18 hours awake at 50% capacity. Option 2 - 16 hours awake at 100% capacity.

It seems a no brainer. But don't get the wrong impression; I lack the discipline to sleep 9+ hours every single night. But I try my best!