Staff note: This post may contain affiliate links, which means Pentax Forums may earn a small commission if a visitor clicks through and makes a purchase. If you would like to support the forum directly, you may also make a donation here.
I discovered that it is very useful.
First setup your calibration device. I used a tape measure and a brightly printed cup. The tripod was set at about 30 degrees, close to the minimum focus distance for the lens.
Establish a connection with the card, set live view off. Make sure the lens is out of focus.
Press the AF button on the camera. It will focus using pdaf.
Touch the LV button on the screen. The focus peaking will show you how much adjustment is needed. A white band shows the region in focus.
Rinse and repeat. Far quicker and easier to see than finding the focus transitions on an image, especially on a small screen. I used my tablet and the large image was very clear. Usually this process requires transferring images to a computer for examination, and the process takes a long time and is somewhat tedious.
Remember to switch out of LV mode otherwise it uses contrast detect which needs no adjustment.