"Block Name" in Custom Template dialogue
You can see this github pull request
There was a forum thread about it somewhere.
Basically it's so that blocks can be accessed in addons by name using
$block = Block::getByName('My Block Name');
So, for example, a stack could be created which contains several navigation-related blocks, but to display them separately in the theme Block::getByName() could be used?
It always feels a little wasteful to me to create an entirely new stack when I know I'll only be putting one block into it (probably silly, I know, but it doesn't feel very efficient!)