Paint/Primer in one... Please explain.?.?

I have been puzzled by this product, just from my understanding of primer and what it does. Is this paint/primer in one just to save time and one step less. I noticed Lowes near me does not sell just paint, it's all paint/primer.
I am old school and will not use this product. I still prep the walls; sand,wipe primer and two cotes of paint.

 

Primers have there place. When trying to cover an oil based paint and such. The newer paints like bears paint and primer in one coat nicer and stick better than early latex house paints. I'd still use a killz or other primer when doing a drastic color change or trying to block a stain. Sand and wipe but mostly your just wasting time with primer now.

 

Its marketing for a thicker than normal paint imo.