The sentiment report shows you how the sentiment varies through your writing. It works by identifying words that convey sentiment and measuring the magnitude of that sentiment. It then works out the average for each paragraph in your piece and shows you a histogram for easy viewing.
Look out for paragraphs with lots of bias words but a neutral or slight sentiment
If you have a paragraph that contains lots of bias words but still has a neutral sentiment then this could mean that you're being inconsistent with your word usage, i.e. you're mixing lots of positive and negative sentiment words. This could cause confusion with the reader. Readers tend to like a consistent message.
Look out for large swings in sentiment
Obviously large swings in sentiment can be desirable sometimes but only when you want them.