Features such as 'Layer Sharing' allows you to quickly update shared components such as headers across multiple pages. Other mockup tools such as Mockingbird will require you to manually propagate changes across all the pages.

From lo-fidelity wireframe, into clickable prototype and then assemble the images for the final hi-fi build as well.

Best integration in a graphics editor.

Offers a side by side comparison of different JPG compressions in real time with magnifier.