Lightning is coming. You have played around with the new User interface, made some reports, and tested out your customizations. When Lightning was released a year ago, it was slow and it was missing things. A year later they have addressed a lot of the issues, sped things up, and now its looking pretty good!
Luckily for us, with all of the updates, we can stay current with Trailhead. Salesforce has been diligently crafting content that not only tells the User what is coming, it also walks you through use cases so you can really absorb it.
Trailhead walks you through the example of using a modal to update a related record. This might not seem amazing, there are little edit modals for everything, but what this example shows you is that you can stay on the same page to update common fields on a related record. Time and again I talk to Users who want to update the Account from a Contact after a call. Now, with a Quick Action, you an edit the Account directly from the Contact avoiding the reload time and confusion of switching between records.