One of the benefits when you switching to Lightning is Utility Bar. Lightning Experience allows you to add your components to the prime real estate in any Lightning app so that your users have one-click access to powerful productivity tools, such as Recent items, Notes, Chatter feed and so on. Your users can access those same productivity tools in a horizontal footer, called the utility bar.
Utility bar gives your users quick access to common productivity tools. The utility bar is a fixed footer that opens components in docked panels. You can add multiple components to the utility bar, each Lightning Apps can have their own set of components in the utility bar. You also can add the same components many times in the utility bar within the same Lightning apps, this is because some of the components allowed you to select a different type of visibility, e.g. for Chatter Feed components, you can select Bookmarked, What I Follow, and To Me feed.
Utility bar will be available and visible for the users, no matter which page they are open, so this gives instant access to the components, this is even better compare to Classic, where you can add commonly used items in the Home page.
As of now Winter '18 release, Salesforce provide 13 standard components available for utility bar, but you can develop your owned components (need to enable My Domain) or install from AppExchange.