I spent day 36 working through the mobile app customization in Salesforce module on Trailhead. The Salesforce mobile app itself provides a mobile experience powered by the new lighting UI which allows you to use Salesforce on the go.
That in itself is cool. The really amazing part is that when you are developing custom applications for salesforce you can leverage the entire mobile experience without really having to think about it too much. If you are using the new lightning UI then you can really “write once, run anywhere” when it comes to desktop, and native mobile applications.
In the module we learned how to customize the mobile layouts to make the experience better for users. For instance, you may only want to add a handful of fields to a record when you are working on a phone. Rather than making your users scroll endlessly to find the fields that they care about, you can optimize the mobile experience with a few clicks rather than recreating distinct UIs for mobile and desktop.