The monograph part list for a bibliographic record may, over time, diverge from the proscribed format, resulting in multiple labels for what are essentially the same item. For instance, Vol. 1 may have variants like V.1, Vol 1, or  Vol. 1 (leading space). Merging parts will allow cataloging staff to collapse the variants into one value.

In the Monograph Parts display:

The undesired part labels will be deleted, and any copies that previously used those labels will now use the prevailing label