Say that 10x fast… (and try googling it…)
I won't delve into too many details here as there are a lot of great resources out there for using the new logging in Sierra, but there doesn't seem to be a place where one of my most helpful system log searches is found online.
^^^ That in Terminal.app will get you the last 24 hours worth of "Previous shutdown cause" messages from the system logs. Useful for troubleshooting.
If you need a handy list of shutdown code meanings and don't have an Apple Training Guide doc handy, this list is very helpful.