I'm sure looking at that blue light around bedtime is also bad for sleep.

Also, why call out Facebook specifically? Any compulsive checking -- email, Twitter, Reddit, etc. -- is bad for sleep because the brain never gets an opportunity to calm down. 

Also: Less Sleep = Less Ability to Focus

Central to the study was a concept known as “sleep debt,” the accumulated difference between the amount of sleep needed and the amount experienced.

Mark said the study’s findings show a direct connection among chronic lack of sleep, worsening mood and greater reliance on Facebook browsing. She also found that the less sleep people have, the more frequently their attention shifts among different computer screens, suggesting heightened distractibility.