In a freemium model, looking at Revenue churn on the $0 accounts would definitely give you a pretty useless metric.
For some metrics it makes sense to lump the two together. But the distinction between the two is helpful for measuring a product's ability to up-sell itself to the existing customer base.
If you're interested in tracking revenue growth instead of customer growth - then say you have -1% revenue churn month/month, your existing customer base is going to be paying you 1% more the next month (even though you may lose a few customers along the way).
For some metrics it makes sense to lump the two together. But the distinction between the two is helpful for measuring a product's ability to up-sell itself to the existing customer base.
If you're interested in tracking revenue growth instead of customer growth - then say you have -1% revenue churn month/month, your existing customer base is going to be paying you 1% more the next month (even though you may lose a few customers along the way).