Every one of the cases I have had to debug in which someone had deleted the localhost entry was someone who had entries for blocking Adobe's licensing servers.
A novice was trying to fix a broken Lisp machine by turning the power off and on.
Knight, seeing what the student was doing, spoke sternly: “You cannot fix a machine by just power-cycling it with no understanding of what is going wrong.”
Personally, I set the host file to use https://github.com/StevenBlack/hosts in order to block ads on every computers I touch.
I also often use software that manage the host file and ignore the default physical file.