Locks to only one editing user and confirms syntax is clean before saving. I'm not aware of nano enforcing correct sudoers syntax. Plus plenty of us don't like nano.
visudo, like vipasswd or crontab -e and other commands, respect the EDITOR environmental variable, so you can edit these files with whatever editor you prefer, while maintaining their protections.
True. Provisioning a new test VM for me usually entails something like this:
ssh in;
visudo;
wtf, this is nano! Boo!;
ctrl-x;
update-alternatives --config editor... :)
