What is the advantage of putting code in a mu-plugin as appose to a plugin or child theme? What is the proper usage for the mu-plugin? I mean I can just put code in my child theme but is that the proper usage? Thanks
Usually putting code in child themes means putting everything in the /functions folder. If you don't write alot of custom code this shouldn't be such a problem.
By using mu-plugins you can create a more logical way or organising your code. Especially on larger websites this will make your life a lot easier. When new devs join the project, they'll actually know where to look for code.