Sometimes I write things grammatically ‘wrong’ on purpose. Grammarly cannot tell the difference between artistic choice and genuine mistakes.
If you are learning English or are not entirely fluent, it is a worthy tool, but so is google docs. I feel the latter does a better job of preserving your voice. Especially considering that, the more you write in English as your second language, your other language fluency will eventually end up adding a lot to your personal style.
In an ideal world, everyone who writes would have a copy editor. I believe having an actual person do the error checking is always superior, because they’re a lot more likely to know what you’re going for.