Why is interpolateTick NOT called on the server?

I'm trying to understand TGE networking but I'm a little confused on why interpolateTick is not called on the server.

I think I understand the basic loop:

1) processTick is called every 32 ms
2) The current tick and last tick are saved
3) interpolateTick uses those two tick values to draw a position between them

This means that what is being drawn is always 1 tick behind the "current" time, right?

Does my understanding sound correct?

Also, back to my original question, why is interpolateTick not called on the server?

Thanks...