Having pdn_disable bit low doesn't influence the communication

In the TMC2209 datasheet it's written that in order to communicate through the UART interface I need to set the pdn_disable pin to high. However I can already communicate through UART, so what is the use of me setting that pin? I've already confirmed that even driving that pin low in-between communications doesn't affect the communication.

Another question about it is if driving the pin low in-between communications will allow the driver to go into standstill current reduction mode? Sadly I can't measure the current in such detail to catch it myself.