One of its main applications is to determine the 3D structure of proteins.
Sometimes you are not able to crystallize the proteins however, and the method cannot be used.
Crystallizing is not simple because:
  • you need a considerable amount of the protein
  • sometimes it only crystallizes if you add some extra small chemical that stabilizes it
Cryogenic electron microscopy can sometimes determine the structures of proteins that failed crystallization.
Often used as a synonym for X-ray crystallography, or to refer more specifically to the diffraction part of the experiment (exluding therefore sample preparation and data processing).
cyclotrons produce the better images, but they are expensive/you have to move to them and order a timeslot.
Lab-based just use some X-ray source from the lab, so it is much move convenient e.g. for a pharmaceutical company doing a bunch of images. The Wikipedia image shows such a self-contained lab system:
Crystallography determination with a transmission electron microscopy instead of the more classical X-ray crystallography.