I'm not sure what doesn't make sense. It's an adjustable roller lifter...it's a tool. You just measure your lifters with pre-load figured in, mock up the tool to replicate your measurements, drop it in, set the pushrod and slowly turn the crank... It's much easier, for me anyway, to not have to deal with the springs.

Since the engine is timed and is running, why would this not accurately simulate how close the valves come to the piston? The valve timing is already set.