I can see something like Grammarly being quite helpful to a non-native speaker, but if English is your native language, do you still find that Grammarly improves your writing?
Although I'm technically not a native speaker, I consider myself completely fluent, and a competent writer. I still find Grammarly or similar services quite useful, even if just to catch stupid "grammatical typos" that a traditional spellchecker would miss. I basically treat it like autocorrect.
I’ve found that it does. It’s easy to forget some of the more nuanced grammar rules, or if you’re spending more time building a sentence it can be easy to lose track of things like maintaining prior tenses.
It probably fulfills a slightly different use case than non-native speakers.