Bothered by the screenshot preview that came with macOS Mojave and acts similar to the one on iOS? The problem is not that the preview appears so that you could edit the picture before saving it finally, the problem is that even if you don’t use this feature it takes a while (a couple of seconds) for the image to appear at the location you set for them (desktop is the default).
I just discovered a solution: to disable the feature completely just open the screenshot program with options displayed using SHIFT-CMD+5. Then in options, disable „Show Floating Thumbnail“ - that’s it. The screenshot will immediately appear on your desktop.