... is to "reinforce" the fibers in that area, help keep dirt (abrasive) out, and possibly create a little lubricity.
A little update: I wound up ordering Griot Fabric Protector this time around.
And an aside: the driver's left side squab and back bolsters are developing cracks that follow along the ventilation perforation pattern. Years of getting into the car in my garage with a workbench in range of the fully open door is the likely culprit.* Since noticing the cracks, I've taken to parking more to the right, and aiming my butt directly onto the squab. I also ordered Griot's leather rejuvenator product as a treatment beyond having used Lexol occasionally.
* Please don't tell me to back in.
I used to be good with all that many years ago driving into Manhattan regularly for school and work, but've lost my touch. The Boxster, particularly the present 981 (as opposed to the 986) has tricky rearward sight lines.