about expansion to P1 unit cells

Hi
How can the predicted crystal structures be expanded to P1 unit cells and again minimised as I have read the following statement from a paper.

"All structures within 15 kJ/mol (higher in energy than) of the global minimum in the COMPASS force field [31]
were expanded to P1 unit cells and subsequently minimized using a cut-off radius of 12 Å."

Reference- Study of Polymorph Prediction For L-Ascorbic Acid. Ali Arslantas-et-al. Int. J. Mol. Sci. 2005, 6.

What is the significance of doing this in my case as I am doing the polymorph prediction of a drug molecule?

Rgds
janhvi