FF lens on apsc, good or bad?

Yes, it will be on a 16mp, either a K30 or K5II-s. I am more concerned that if I get the new K5, I want to get a very high resolution lens (only one for now, more as I go). I found some MTF resolution charts so I can see the numbers but I am still unsure how it works when cropping only the center of a lens. It seems logical that using the entire glass would result in using more lens resolution, but if this is not true please set me right.