Question about what is jumpstarting a chromebook?

Hello,

Just started my new job two days ago, we were updating policies for chrome books. First we take them out the box, and then one tech has a usb battery with a power cord. He plug in each chromebook and pulled out very fast and he did this to all of them and then the chromebook started to boot. Anybody know why the jumpstart is required? Or can help me understand the process. Thank you.