If you use Sketch to draw your interface, you get @2x exporting and slicing is built in. It hurts my head to think about what I would have to do if I was using Photoshop.
* Scalability - you can resize a button and get the correct look
* Simplicity - you don't need to create 1x and 2x resources
Downsides are that it can be slow and it muddies up your code base.