YAMLMerge in Git

So I was looking at this page:
http://docs.unity3d.com/Manual/SmartMerge.html

I was going to set up my git to use YAMLMerge tool as the docs say. But correct me if I misunderstanding, but isn't the way Unity saying to configure this, won't that make git merge ALL files, even C# files with YAMLMerge?

Isn't that undesirable? Or does YAMLMerge deal with C# files?

Or how do I set up YAMLMerge and git to only merge YAML files?

Also, should meta files be merged with YAMLMerge ideally?