WordPress updates are primarily for any security weakness. Once a new version is released it can spend weeks being tested out in the real world and that’s when tiny bugs are discovered (and suitably admonished).
So when you see a banner heading in your dashboard for the ‘latest update’, just ignore it. I like to wait for a good solid global test run to have everything working properly.
WordPress 3.9.1 is happy, healthy and strong. Well worth waiting for.
And well worth watching the video for an introduction to the bells and whistles.