It's good at spotting stuff, like:

* Overusing verbs

* Poor structure

* Bad transitions between grafs

* Passive voice

And even bigger-picture stuff, like "you might want to zoom in here" or "this section isn't paying off". I've only in the past few months started using it for proofreading, and it's pretty solid.

But if you take any of its words, you're infecting your writing with Claude's tone, and it will show.

It's super useful as a reader of your writing. It's a terrible collaborator, unless you're writing for an audience of middle managers.