Protip: the quality of any metric used to measure performance will ultimately degrade over time, as the metric itself becomes the target for optimization instead of actual performance. any metric can be gamified
Yes - people start optimizing on the metric, and metrics where correlation doesn't imply causation degrade. The other thing I've seen is competitive pressures degrade metrics. If "A customer using us for X is 95% not likely to churn" is true in 2015, competitive pressure will push it to 85% in 2016, and 75% in 2017.
"When a measure becomes a target, it ceases to be a good measure."
https://en.wikipedia.org/wiki/Goodhart%27s_law