so that an individual program section can be replaced, and other parts of the program updated so that relocatable addresses and other references can be corrected by the linkage editor, as part of the process.

One advantage of this is that it allows a program to be maintained without having to keep all of the intermediate object files, or without having to re-compile program sections that haven't changed. It also permits program updates to be distributed in the form of small files (originally card decks),