Like many others, I'm sure, the company I work for builds email campaign designs in photoshop. We have always used layers straight on the canvas and the crop tool to "splice" (without using the splice tool) images into however many sections necessary.
We are working to create a more streamlined process by combining multiple files into one, we are doing this by now utilizing artboards. The only issue we have ran into is that artboards do not allow for the crop tool, or at least in the same capacity as before. When you crop/resize the artboard, you can not see the surrounding area behind a semi-transparent overlay. This would be a small addition that would help us immensely in cropping our designs quicker and more accurately.