Bookmarked Relative Font Weights Considered Harmful by Den McHenry (denmchenry.com)

Not exactly, but who can resist writing a "considered harmful" article when you can get away with it?

The real harm is that you can very easily conceal the semantics conveyed by font-weight depending on the font that's rendered, which is not always in your control. This all depends on how you define the base weight to which your relative values refer, and (1) whether that base weight is actually available in the rendered font and (2) which value is substituted if it isn't.