Why Rolex Service Center opened my watch back case?

[alvinthz]

I sent in my watch to replace Screw link pins for Rolex straps bands bracelets links.

the person in charge told me that the waiting time was an hour to remove 5 new link pins. Which is quite long. I can do it in 5 minutes.

Upon delivering me back the watch with 5 new link pins, I noticed they actually opened my watch case.

When asked why they said is the process to check if everything is working correctly.

I told them it is the only issue with the link pins because the watch shop I went to damaged the pins upon removing one link to suit my wrist size.

Again, my watch is brand new. Really don't understand how the link pins are related to the watch movement until needed to remove the back case. Is that even necessary?

Is anyone facing the same as me? This is done by ROLEX SERVICE CENTER anyway. Kindly share your experiences!