The worst possible Performance metric

Developer performance is not easy to measure.
Why is this? Because a developer's primary objective should be to find the overall simplest feasible solution towards unsolved problems (or at least, "un-implemented").
However, time and again, there are non-technical project managers who try to do it.

There is an infamous telltale project where allegedly one million lines of code had to be written within one month, but the developers overperformed - producing even one and a half million lines!
Wow, what a great result!*

Refactoring is a technique primarily focused on eliminating code complexity, therefore increasing readability, maintainability and improving overall design.

Story time:

One of these days, my team was challenged with automating a business process.
Occasionally, the customer would ask how we were doing. So, one glorious day, they asked very specifically, "How many lines of code did you write today?"
It was probably the worst possible day to ask this question.
The entire team had written maybe 10 additional lines of code - but deleted roughly 200!
So, at the end of the day, the "lines of code" metric was 190 in the negative!

It actually took a while to explain to our customer why they should still be paying for this ...

The refactored code eliminated a performance problem.
It also implemented 2 different user stories from our backlog.
And in all that, we increased the flexibility of the current code base way beyond the customer's need - with no extra effort!

Lesson Learned

Never, ever let anyone measure developer performance in "lines of code". It is not a success metric.
Don't even go for "tasks done" or "amount of user stories completed", these are all deceptive!

The only metric that should be applied to software development is "outcome".
And that one is incredibly tough to quantify.
In the end, all it means "How much better is the software fit for it's intended purpose now?"