Is there a situation in the English language where the "less" vs "fewer" distinction matters?

@mikeburns technically fewer is used only for things you can count and less is used only for things you can't count, but honestly, and this is coming from a former grammar stickler: language is a living thing, people will know what you mean if you use either in conversation, and it will only really matter to someone who prizes grammar conventions over communication and fellowship.

@checkervest
I was staring at a PSA on the train this morning that mentioned "one less worry" and my first thought was "probably should be 'fewer'" but then I wondered: when will we stop caring? Are we already there? It's a grammar rule that doesn't seem to resolve any problems.

@mikeburns plus the two words have been used interchangeably for hundreds of years. The only reason the rule is there is because someone in the 18th century thought one usage was more elegant than the other.

@checkervest @mikeburns ... Huh? They are not used interchangeably and never have been. You cannot be "fewer happy," you cannot run "fewer fast," etc. It literally only works in the opposite direction. Fewer is 100% exclusively used with count nouns, without exception.

@noxy @mikeburns I'm sorry, I should have been clearer: the classic less/fewer grammar issue comes up specifically when used in a situation where counting is required. You can't run "fewer fast," but you can either "run fewer miles" or "run less miles" and you would technically be correct.

@checkervest @mikeburns Technically you *wouldn't* be correct, but it would still be fine make sense. That doesn't mean the distinction is useless and should be done away with.

@noxy
Having read more into this I must ask: in which way would you technically not be correct? (And, apparently, in which year?)
@checkervest