Here's this link about logs vs metrics, which makes lots of sense.
And also, a post about logging levels, and how a very basic rule serves for it deciding which level means what. Very useful info in the associated reddit thread.
- DEBUG: information that is useful during development. Usually very chatty, and will not show in production.
- INFO: information you will need to debug production issues.
- WARN: someone in the team will have to investigate what happened, but it can wait until tomorrow.
- ERROR: Oh-oh, call the fireman! This needs to be investigated now!