I take this advice like "do not use a preposition to end a sentence with" and "pay close attention to 'much' and 'many'". Personal preferences from the 1800s taken as gospel by grammatical extremists, to the point where they're taken as some kind of solid rule in a vain attempt to forcefully shape language to a personal preference.
There are cases when you want to follow certain guidelines, for sure. If you write for a publication that adheres to Meriam-Webster, you'd better stay consistent and figure out the right AltGr code to type the right dashes. However, for the 99.99% of written media today, none of that matters.
> Personal preferences from the 1800s taken as gospel by grammatical extremists, to the point where they're taken as some kind of solid rule in a vain attempt to forcefully shape language to a personal preference.
This is also true of "less" and "fewer". I use "less" everywhere.
Ending sentences with prepositions is and had always been fine. It has never been a serious rule of grammar that you may not end a sentence with a preposition. It does sometimes make a sentence sound better to rewrite it so that it doesn't end with one though. For example, "do not use a preposition to end a sentence with" sounds awkward to my ears, probably because you deliberately crafted the sentence to end with a preposition even though that is not naturally what you'd end that sentence with. (The previous sentence doesn't sound awkward to me, interestingly.)
Getting "much" and "many" right is completely different. They mean different things. Confusing them makes you sound stupid. Less vs fewer is the same. It often doesn't matter but in some cases it really grates on the ears (eg "there wasnt much people there" just sounds awful).
Dashes are not in the same category. They are orthographical conventions. They aren't really grammar. They are more like spelling. You can spell things wrong and say it doesn't matter because spelling is arbitrary and you can use the wrong dashes too, but it makes you look either uncaring or ignorant. If you want to give a good first impression, learn the basic conventions of written English and follow them.
There are cases when you want to follow certain guidelines, for sure. If you write for a publication that adheres to Meriam-Webster, you'd better stay consistent and figure out the right AltGr code to type the right dashes. However, for the 99.99% of written media today, none of that matters.