As indexed files are updated by adding, deleting and altering records, the index and data structures become disjointed, making processing less efficient. In addition, space left by deleted records is not always reused, making the file bigger than it needs to be. After a large number of changes have been made, it is worth reorganizing an indexed file. By ensuring that the input and output file settings are identical, the data and indices can be rebuilt in an ordered sequential manner, reclaiming any free space, and so providing optimum file performance and integrity.