Using Code Coverage with Manual Testing

https://blogs.msdn.com/marcalt/archive/2006/07/02/654157.aspx

A good thing to remember about CodeCoverage in VSTS... however I wonder how to evaluate this metric because "manual testing" is slow...

I don't think you could reach more than 20% CC with manual testing in a reasonable amount of time, and how do you ensure to test the new functionality while new features are included?