1. When the screen color changes at sunset it's a subtle but powerful cue to know that the work day is coming to a close. And then if I'm on my computer when it changes around bedtime that's a cue to GTF off the computer.
2. All the science I've read suggests removing blue light in the evenings does indeed help with sleep. So why not use it?
Unfortunately in northern latitudes, our sunset can be as early as 3PM or as late as 10PM, so it doesn't quite work for that purpose here!
Nevertheless, I find matching the colour temperature with the time of day makes my eyes far more comfortable.
The studies on whether blue light messes with sleep are mixed, but I personally find if I set my lights brighter and bluer in the morning that I feel more awake than I do otherwise.
Yeah, that makes it totally unusable for me, it's ridiculous that they don't let the user set the hours and insist that you must follow the sun, because that's "more natural". Even though that might be true, it's totally impractical, you can't organise your work day after the sun, that's totally incompatible with the rest of society. At least os x night shift let's you set the time like the responsible adult that you are..
I've used f.lux for a long time, but it kicks in in the middle of the afternoon in winter and probably about bedtime in summer!