Does x matter? They ask rhetorically, with tired innuendo. Well, it depends on the context, however here is a very short guide to what may and may not matter in the eye of the beholder. The test is simple: is there a word for it? There is a reason why 'height' is a nice short and ubiquitous word describing a person's length when lying down as well as the distance from the top of their head to the ground when upright, while the speed by which one's fingernails grow is yet to be described with a word of similar recognition. That reason is that height does matter to enough people for there to be a word for it. Fingernail growth speed might be an equally good marker of adequate nutrition and genetic potential, but it is yet to achieve widespread recognition as such - and as a consequence become endowed with a word that would neatly describe it. (Some might argue that being described with a word predates the prominence of a metric, but that's just a useless chicken-and-egg debate.)

So there you have it, the rule that I am yet to see disproven is that what can consciously matter, at least commonly, within wider society, has to also be described with a word commonly understood within that society.