[rainer]

Yes! It does make total sense. So" Lets say an the full blown image was that with a 72 ppi.
If i was to crop a section out from a whole image lets say to an 8x10........then there will be fewer pixel squares with 72 ppi in each of them. Because fewer pixel squares have now become more visible i there for need to increase the pixels in each square inch of that image.
So" I understand that ppi becomes important when cropping down to a particular section of an image to achieve a particular size.
That is how it all makes sense to me.