As far as using nemo to provide use of the Desktop it wouldn’t need patching if you can get an appropriate file into /etc/xdg/autostart.
In that test ppa I did that via a symlink in the debian file.
The reason for patching it was to allow it to show up in startup applications, also removed the OnlyShowIn= line, whether that mattered didn’t bother to ck.
The other reasons to patch nemo were to give it useful desktop actions compared to default couple (likely missing some translations in the added ones), give it a name different then nautilus and an icon different than nautilus.
The 3rd patch was for one of the supplied extensions which is by default is non-functional in an unity session.
So all in all rather insignificant other than getting nemo-autostart to run on login.
Any user that wants to use nemo as their main or only file manager can ‘improve’ their experience on their own after the fact.