With Adobe Photoshop there are lots of methods of doing the same thing, whatever you're doing, and some may be more destructive than others. Saving work, after using a non reversible workflow, may result in an factors that you will no longer be able to adjust.
A good example of this would be when isolating a subject in one image, to then transfer into another image. We can open up our subject image and, using the eraser tool, delete the surrounding area to be able to then drop our subject into the destination image. Once we've done this however, that background is gone. There is no way of reversing this effect if we then save the .psd as the history tool will not allow returning to states in a previous save.
Instead, working non destructively, we can duplicate the background layer and instead work on that. Keeping the background layer below all the other layers, and placing the background layer clone above, we can work above these two layers and preserve the original image. In the below image I have used the quick selection tool to isolate the subject then rick click and Layer via copy. This creates a copy of the selection that we can do what we want with, we can use high magnification and eraser to fine out the edges, but we are left with an untouched original with a copy of the selected subject we can now copy onto other images.
Adding adjustment layers is also a good way of working on colours or noise related factors without adjusting the original images properties. if we add a contrast adjustment layer, we can change the contrast of the dark and lights in the image and using paint brush or selection tools, even highlight specific areas to apply fixes to. And again, applying the technique mentioned earlier of duplicating the background layer, we can work in a protected environment.