Pros:
Excellent online grammar knowledgebase
Another line of defense for authors who self-publish
Useful for non-native English speakers and new writers
You can switch between US and British English
Grammarly helped me identify:
Confused prepositions
Overuse of the passive voice
Wordy sentences
Repetitive words
Common writing mistakes like misplaced apostrophes
Spelling errors
I strongly recommended people to use Grammarly Tool