How is having class="mw-50" different from style="max-width: 50%"? Same goes for the majority of classes I looked through in the css file. I cannot think of a difference other than a cosmetic one. I would argue that the latter is easier to read and remember, and just as easy to type with the right text editor plugins.

You have precisely the same disadvantages:

• You tightly couple your document structure and your style guide and therefore make it much more difficult to maintain. (Imagine doing a complete redesign of a website built with tachyons, or a css-zen-garden where the template was built with tachyons)
• You lose the flexibility to change the properties of multiple related elements at the same time:
• You clutter up your DOM with styling directives