In the artical of Style Tiles: An Alternative to Full Design Comp, it illustrate the reason of using style tiles is becaue that you can present clients with interface choices without making the investment in multiple photoshop mockups.
###Issues with Photoshop Mockups The issue with full-designed Photoshop Mockups is that they are not scable at all. It takes at least 2 months to fully impletment the site from the concensent of the mockups with stakeholders. And during that 2 months, a lot of things can hanppen.
I worked with a web agency to resigned our company website before. And during the design phrase, they presented us with some really beautiful Photoshop Mockups. They were really great, very pretty. And we were so happy about those.
But the issue came after the whole website was implemented. We wanted more features. We wanted more robust features because of business growth.