Why does Android need this? Does the OS not let you control notifications?
DoNotNotify gives granularity and rules (which a specific app may have chosen not to implement).
For example:
"Allow <budget airline app X> to display notifications of gate changes"
"Block <budget airline app X> from displaying advertising notifications"a) bundle everything in one category, from critical notifications without which the app can't fulfill its purpose to "HEY YOU HAVEN'T USED ME IN A DAY, USE ME NOW" spam
b) create a new category for spam every time they feel enough users have turned off the previous one, which is often