Mostly to tell me when my well pump or pressure pump starts / stops, but also events from BlueIris (video) when it recognizes things on camera (its my cheap motion detector lol). I also get notices when maintenance starts / stops on my websites, daily visitor stats and some other metrics I like to keep tabs on. On that note also a ton of notifications from my various web services are sent over NTFY.

Has to be KVM based. Then I look at shared / dedicated CPU cores and IO disk speed.