I use systemd and its timers to run various tasks on my machines on a regular basis, and since that's all happening in the background, I want to know if those jobs fail. Now, it's better to have a job-specific alert rule that checks that the state of the world is desirable (for example - instead of checking "did the e-mail backup job succeed?", check "is the most recent file in the e-mail backup destination less than 24 hours old?"), but it's nice to have the general "did the service succeed?...
