Without being technical, I'd say visualise a bikes dirt tires versus road tires.
On the dirt tires, there are tread blocks and on the road, more flexible rubber with grooves... a lot more detail.
It has knock on effects such as temperature, but in essence it adds another layer of feeling, and a very important one.
That phenomena of no grip in low speed corners highlights the enhancement well.
Before, the tire might slide naturally, but you could not feel it. Experienced sim racers knew they were missing information, but were able to 'fill the holes' so to speak.. Now everyone can feel what was missing, and it's calculated in extreme detail.
Essentially, if you try one of the older cars before it was CPM'd it would feel kinda the same (more calculations and less ballpark figures) except it 's like half the detail is missing as you turn in or light up the rears.