It is to keep the contact surface of the rocker centred under the cam lobe. 

If you did not thicken the lash pad, the adjuster would have to go higher and tilt. This will affect the so-called "wipe pattern" and the lobe may roll off the correct region and get damaged every time it rotates.

Fig.1 Measuring

Fig. 2 Good Wipe

 

Fig3. Bad Wipe

Very nice explanation Blue.   Whoever did that re-grind in the last set of pictures looks like they did a beautiful job. Who was the Vendor?

thanks. things are starting to click