Hemingway makes your writing bold and clear. It's like a spellchecker, but for style. It makes sure that your reader will focus on your message, not your prose.
Too often, our words are like our thoughts — innumerable and disorganized. Almost any bit of writing could use some cutting. Less is more, etc. So, the Hemingway Editor will highlight (in yellow and red) where your writing is too dense. Try removing needless words or splitting the sentence into two. Your readers will thank you.