From the site:
#The Purpose:
I have been looking for a good guide to build a TimelapseRPi that runs on battery and with a safe way to shut down the Pi after ‘photo session’.
I found out pretty early that just pulling battery plug from Pi when done capturing pics can very effectively brick the USBkey I’m using for storage. In order to mend this I added a Tactile button that, when pressed, initiate a clean ‘shutdown’ on my Raspberry Pi.