There’s info in the Install Guide (around p125)
It has to be enabled before it can be downloaded and you have to have admin privileges to install it.
IMHO, the Edge Client service is a move towards on-prem operations. Now there is something to install, and kept up-to-date, and it brings with it a level of security exposure since it can write to local storage. I believe that @edge (no relation) hinted that this might move to a web worker where the browser has a background thread checking for printing much like the current System Monitor running in your system tray. If they give the client Progressive Web App capabilities, then you get the web service worker automatically and potentially add some offline functionality.