There's been a few sites I've used WYSIWYG editors on recently where I've run into the issue of needing to disable it on certain text areas. TinyMCE supports this with a theme override just fine, however, it's not so simple when you have multiple text areas with the same name.

Take the node edit form. For every node type, the body uses the same name.

A practical example of when you would need to disable a WYSIWYG editor would be when filling a node body with previously designed HTML like when you design an HTML Newsletter.