1. You edited it by hand and fucked up the syntax. In this case git could print an error instead if offering to add the username/email.
2. You deleted itself. When git asks you for the username/email again it'll actually tell you that that file was for storing the username/email.
3. Filesystem error. A faulty gitconfig with be the last thing the user is worrying about.
All in all I don't see how all of this would imply that prompting a username/email isn't a good idea.
1. You edited it by hand and fucked up the syntax. In this case git could print an error instead if offering to add the username/email.
2. You deleted itself. When git asks you for the username/email again it'll actually tell you that that file was for storing the username/email.
3. Filesystem error. A faulty gitconfig with be the last thing the user is worrying about.
All in all I don't see how all of this would imply that prompting a username/email isn't a good idea.