The point is adjusting the line of sight through then out of the scope to align on target close to where the barrel axis aligns before the first shot's fired.
Scope mount ring's axis is often several MOA off from bore axis. Sometimes the scope's LOS axis is not aligned on its outer tube's axis.
"Boxing" your scope with a collimator is much more precise than shooting bullets. Plus, the slop in angular change boxing a 1 or 2 click square is easily revealed. As is the reticle slop revealed zooming variables across the power range.