The problem occurs when you are SSH'ed to a machine you are setting up, or one that is customer owned, you use whatever editor is around to make a quick edit, not realising that the file labeled .conf is actually a YAML file, you hit tab because it makes logical sense and then shit breaks.
No thanks, YAML is a terrible choice for configuration files.
If you're connecting to a machine over SSH and you're making enough changes that it's going to be difficult to maintain an indentation scheme, open it up on a local editor with SFTP. Emacs supports it out of the box, and Sublime has an excellent nagware SFTP package in the standard repos.
All YAML files are required to begin with "---". If you're aware of what YAML is, and you've seen YAML ebfore, and yet you somehow "aren't aware" that something is a YAML file, you're incompetent.
No thanks, YAML is a terrible choice for configuration files.