As in many other areas of molecular science, symmetry is a very useful tool in crystallography. An example of one of the important applications of symmetry is illustrated by the X-ray photo displayed here:

In the photo, it appears that there is a regular geometric relationship between the intensities ( there seems to be some “four-ness” involved). If the molecular structure is eventually divulged by interpreting the intensity distributions in a series of photos like this, perhaps not ALL the data have to be measured. Maybe only ¼ of the data will suffice.