In a nutshell, it will make your workflow faster. Adding and activating new themes or plugins on your site should be a lot easier. Because everything happens on one screen, you will never lose your place when performing above mentioned tasks.
‘Pepper’ has a lot of improvements in the editor itself. For example, if you have a broken link inside your text WordPress will let you know about it and allow you to update the link before publishing. If you happen to lose internet connection while writing your article, don’t worry! WordPress saves everything locally to your browser. When you return to edit it notifies you there’s a more recent draft for you to work, so nothing gets lost. WordPress dashboard now uses the same native font as your operating system which means pages load faster and overall performance is improved.