Joel says he starts out in Adobe Photoshop Lightroom 4 (LR4) and, once he's done some initial adjustments he send his images over to CS6 as Smart Objects (Photo/Edit in/Open as Smart Object in Photoshop). Excellent! Way to go! As soon as he gets the image into CS6 as a Smart Object he immediately Right Clicks on the Layer box (where the Layer name is, but not on the name) and selects New Smart Object Via Copy. Again, excellent! Way to go! That step is very important. You can't do it right by using the keyboard shortcut CTRL J. It may not sound like there should be any big deal, but, there's a big difference.
If you do a CTRL J and copy the Smart Object you end up with a clone of the original Smart Object. Whatever you do to one is replicated in the other. That's not what you want. Doing the New Smart Object Via Copy breaks the two Smart Objects into independent items. You can totally screw up one and the other is unaffected.
In today's image the ground portion of the image was lightened in one Smart Object and the sky darkened using the other. Double Clicking on the Smart Object icon in the Layers Panel (the thumbnail shows up with a small insert icon in the lower righthand corner, denoting it as a Smart Object) will open Adobe Camera Raw (ACR). ACR "is" the Develop Module in LR4. All edits are nondestructive. With the first Smart Object open in ACR the ground area (the rocks, the lighthouse, the trees, etc) was lightened and the contrast increased. Once the adjustments were made, the Okay button was clicked. The second Smart Object was the sky. It was darkened and the Clarity reduced just a bit. The Okay button was hit for that one. Now I had one bright and one dark version of the image. A Layer Mask was applied and painted in with Black to conceal the changes made to the sky. Today's image is one of the easiest you'll ever find to paint on a Mask. The entire interface between the ground and sky is a silhouette. It couldn't be easier.
Joel Grimes does similar things to his images. Naturally, since he's typically doing portraits and stadiums and such, the specific process he'll go through would be different than what I just described.
Here's where I cringed when I saw what he did next. He merged his two Smart Objects. NO Joel, SAY IT ISN"T SO. He just broke the chain that is the essence of using Smart Objects. He can never go back to the start and make additional adjustments in ACR on the original Smart Objects. What (in my opinion) he should have done was make a new Smart Object out of the two Smart Objects. (Control Click on both Layers, then Right Click in the Layer box and select Convert To Smart Object. This would give him an editable "Merged" copy of the work he'd already done.
You have to remember the analogy of Smart Objects being containers. Let's say you're working on two projects. You have one box for each projects. You layout one project to the left of the boxes and the other to the right. (For some reason you need to keep the projects separate.) You work on one, then the other. Back to the first, hit a stopping point and switch back to the second. You keep working like this until you go as far as you can and need to move on. You put all the components of project one back in its box and all the pieces of project two into its box. In order to carry both projects to their next step, put both into another box (make a new Smart Object with both original Smart Objects). Move on. If you need to (for some reason) merge some other item with one of the Smart Objects, do it as another Smart Object. When that part is complete, make those into a Smart Object. You can go on all day with this process and always go all the way back to the original image in ACR and make adjustments.
The big trick (and I've said this several times) is (once you gotten as far down the list as you need to go) to work your way back up by saving and closing each Smart Object. (File/Save then File/Close) Do not use Save As. It's File/Save - File/Close for each Smart Object.