If you've been around Photoshop for a while you have probably been pounded with the idea of using Smart Objects and Smart Filters. Kudos to you if you're using them, but if you're not you're probably getting pretty frustrated when you have to change an adjustment or effect you have made to the image. Particularly if it was pretty intense and you can't remember exactly what you did. That's what makes the Smart Objects and Smart Filters so useful.
Let's start by explaining what the Smart Objects and Smart Filters are. The idea of these is to preserve the original data so any adjustments are non destructive. Therefore, when you convert a layer into a Smart Object you are asking the system to remember the original layer information and the effect each ensuing adjustment has on that information. If you use a filter to make these layer adjustments the resulting changes are created as Smart Filters. So the variables used in the filter (ex. number of pixels in a Gaussian Blur) are saved in the filter adjustments and you can always go back and make changes to them. Even if you have made other filter adjustments afterward. The cool thing is that this change will be made to the Smart Object including the effects of the other filters. So if you do a Gaussian Blur and then a Render Lighting filter you can go back and change the Gaussian Blur and the effect will be on the entire object, including the Render Light filter. Without the layer being a Smart Object with the embedded Smart Filters, this would not be possible.
So the idea is to convert your layer to a Smart Object first. Then apply your filter(s). The filter will automatically become a Smart Filter and be layered within the Smart Object. So if you apply multiple filters they will all become Smart Filters within the Smart Object and will each be non destructive and editable. This also includes most filters from Photoshop Plug-ins (ex. Topaz, OnOne, Nik, etc.).
While this is very cool, there are some things you need to know. Smart Objects do not allow certain adjustments. Anything that alters pixel data cannot be done within the Smart Object. For example, you cannot perform adjustments such as painting, dodging and burning, or cloning. To do these operations you will first have to copy the Smart Object layer, convert the new layer into a regular layer (rasterize it), and then perform the operation. Performing these operations on a layer mask may be a good option to maintain their non destructive nature. Also, in the past some of the Photoshop filters could not become Smart Filters. However, this has changed over time and most can now be converted. The only one I am not aware of at this time is Vanishing Point, but there may be an additional one or two that I am just not aware of. Should this situation occur, the filter will not be available (it will be grayed out on the menu) when you try to select it while on a Smart Object layer. To use these filters you will have to copy the Smart Object layer, convert the new layer into a regular layer (rasterize it), and then apply the filter. Again, you may want to use a layer mask to maintain the non destructive nature of the layer.
This message box will appear if you try to use an editing tool that is not allow for a Smart Object
Even with these limitations your use of Smart Objects and Smart Filters will enhance your ability to non destructively make edits. This approach will save you time and frustration by not requiring you to recreate an effect or adjustment.
Finally, new in Summer of 2014 is the ability to link Smart Objects to other instances where a different image uses the same Smart Object. This means that if you are reusing the same Smart Objects in other images you can choose to have any updates to the Smart Object in one image automatically update the Smart Object in the other images where it is used. This can be huge. Especially if you are using a common object in many image files. Imagine a client logo that is being used in all of their images. Suddenly they want to add a small tweak, such as adding the Trademark emblem. If you have the logo in a Smart Object and they are all linked all you have to do is update it in one image and all of the other images will be updated automatically.
It took me a while, but now I am converting and using Smart Objects and Smart Filters everywhere. Try it a few times. I think you be convinced as well.
Hope you found this helpful. Happy shooting.