Who can can spell synecdoche? I certainly can't. I just look up the word each time I need to use it. Spelling is trivial. Misspelling, on the other hand, is far from trivial. In other words, nobody cares after the third grade whether you can spell a word in a spelling contest. People only care if you don't spell something right. You don't look smart for spelling things right; you only look idiotic for not doing so.
A lot of other features of scholarly writing are like that: if you get them wrong they are distractions, but if you get them right, your paper just looks normal. You don't get extra credit for just doing basic things correctly.
If you are a student you might want to not
--spell the professor's name wrong.
--put a grammatical error in the title of your paper.
--use a word from the list of the words your professor told you never to use.
--get the name of the main character in the novel wrong.