It's a handy feature to keep even if you're not in a team environment. You could still do with the notes, but not upload them remotely.
If you're in a team, this is critical to maintain sync.
Unchecking design-notes will not stop creating these folders. If you're keen on still doing this, follow these steps:
- Go to "Manage Sites" in the site dropdown list
- Select the site you want to remove _notes folders from
- Click "Edit"
- Click "Advanced"
- Click "Remote Info" in the Category list
- Uncheck "Maintain Synchronization Information"
- Click "Design Notes" in the Category list
- Uncheck "Maintain Design Notes"
That will disable creation of _notes folders for your site.
If you want to delete all _notes folders for your site after you've chosen to stop creating new ones, click "Clean Up" button once.