Sometimes you forget to submit especially if the only change was to mediatype.

You might have scanned covers at greater resolution locally than the global profile.
It would be nice to track such differences.

Sometimes you make a local change on a locked title or a change that is not very useful like Blu-ray mapping for tv-series.

My DB is probalby tiny compared to some but it has almost reached 400 titles and I'm sure there are some local changes I'm not aware of.