A good example is when you're dealing with third party APIs. They break, a lot, without you really knowing why and often not really knowing how they're going to

A good example is when you're dealing with third party APIs. They break, a lot, without you really knowing why and often not really knowing how they're going to fall over (even google's, one of our reports using the Adwords API fell over last week because it was returning 500s for an hour or so and then just worked again). So say you're doing an hourly sync, and it falls over, you want to log a warning. It happens, no need to send out the fire engines. If you're getting a warning every hour, that's "too many warnings".