Suppose that you are switching to a new system, and you want to know that the data you have transferred is intact and 100% identical to the files you started with.
Data means image files, Lightroom catalogs, spreadsheets, mail, word processing files, videos, databases, etc—anything that you create and has value to you.
IntegrityChecker can take the worry out of this process. IntegrityChecker can verify any files on which it has been run before, even without the originals (there are alternatives such as “diffing” source and backup, but those are far slower, and require the original and the copy).
Some pro photographers burn DVD or BluRay discs containing files with IntegrityChecker support; these discs can be verified at any time. There are numerous such uses.