Could someone explain the appropriate setting for the crossfader?

Hi all,
Just bought a Pioneer DDJ-Sx2 (to use with DJay Pro 2 and my Macbook Pro) and there is a knob to control the crossfader curve on my controller.

I don’t understand how this works. I googled this a lot but I don’t understand the difference in volume that I get depending if the knob is on the left hand side or on the “picnic table” side.

I mix pop songs, old disco, top 40 and occasionally an EDM song so no need for very long transition. Most of my transition take place over 16 beats.

What setting do you recommend? Left? Middle? Right?
If I set the crossfader curve in the DJ Pro 2 settings and I turn the curve knob afterwards, will it change the Day pro settings?

And if someday I want to learn scratching, could I still scratch with the setting you recommend?

Thank you!