It is reasonable to use as an indicator of scenarios where you should pay closer attention. If someone produces an unusually high amount of code, that might in

It is reasonable to use as an indicator of scenarios where you should pay closer attention. If someone produces an unusually high amount of code, that might indicate that they are producing a lot of functionality, but it might also indicate that they are churning out mounds of crappy boilerplate that should be abstracted better. If someone is producing an unusually small amount of code, that might indicate that they are very unproductive, but it might also indicate that they are very efficient and are finding simpler ways to express functionality. All of these things are things that you want to be aware of. The mistake is treating metrics like this as something that is correlated directly with performance instead of just tools to help you understand the bigger picture.