Earlier quoted context omitted.
What do service workers restrict as compared to the previous model?
The main issue is that their lifetime is limited and they're getting constantly killed. This happens all the time even when the service worker is being actively used.
It's a headache early-era iOS developers are familiar with, but this move is basically Chrome team saying "We've watched the community try to implement responsible resource handling, and they suck at it, so we're taking some of their choices away so that the browser can manage resources for the user." Because battery matters.