If you know you "need" .800 net lift at the valve(for example), then you would have a cam ground with enough lobe lift to get you there....... After flex/deflection and lash.

That's fairly common practice for a high level build.

Not all rockers have the same level of rigidity, and not all rockers are built with the exact ratio.

For example, the last set of 1.6 HS rockers I checked were 1.67 unloaded, and were still slightly over 1.62 with 700lbs of pressure on them.

I had some Hughes 1.6 rockers that checked out at just under 1.6 unloaded, and were down to 1.51-1.52 with 600lbs of pressure.

You need to know what you have to know how to get where you want.