The diffraction pattern consists of reflections of different intensity, and a lot of patterns need to be collected to cover all necessary crystal orientations. After some data processing, we end up with a list of indexed reflections and their intensities . The diffracted X-rays are scattered by the crystal at a certain angle. The further backwards the x-rays scatter, the higher we say is the resolution of the data set . The extent to which the crystal diffracts determines how fine a detail we can actually distiguish in our final model of the structure.
High resolution is thus desirable.