With a normal, functioning sleep cycle, or sleep/wake patterns that are predictable or manageable, there's little benefit besides the cool factor of tracking everything. Some of us have sleep issues, whether environmental or biological that we'd like to understand and manage better. I, for example, have been diagnosed with non-24 hour sleep disorder. The treatment is basically cycling through sleeping pills and amphetamines. I think the necessity of that is absurd and would rather find better ways to deal with it (like having alarm clocks actually work. I have a 50/50 shot of not waking up when my alarm goes off and instead wake up hours later with it having been going off the whole time, even when I would have had plenty of sleep). That being said, the technology is still very primitive and expensive for what it provides.
