When I was a kid we were taught the difference between metaphors and similes. When I was an English major in college my professors spent time going over that information again and it was on important exams. As a teacher I've often seen curriculum teaching the same information to kids. And, of course, as a professional writer I'm expected to know that information.
Both of them are used to compare things, but it doesn't really matter if people use 'like' or 'as,' or use other comparisons that leave those words out. It's still obvious that things are being compared.
Lots of grammatical information really does matter. If a sentence doesn't have both a noun and a verb it doesn't communicate the intended information, and confusing adjectives and adverbs can make it obvious that a speaker doesn't know the English language well. It's important for students to have basic knowledge about how our language works.
But I have a big question about the difference between a metaphor and a simile. Why in the world does our education system spend so much time on such a small distinction? The few people who are fascinated by grammar might consider the difference important, but when it comes to communication between ordinary people, who cares?