[Logician]

When you query the db the result is saved inside an resource (think it as a structure similiar to an array) so takes space in memory. After you processed the result within your "while fetch array" loop, you assign its values to a "real" array and at this point you are finished with your resource. So to save some memory space its suggested to delete it from memory as you dont need it anymore and free_result object does exactly this..