I have been experimenting with Luminar 4 for replacing skies, and it's truly amazing. Without having to make precise selections, you can add a new sky behind many types of subjects flawlessly and in seconds. I had this picture of two roseate spoonbills in Florida against a bland sky, and in about 5 seconds I was able to replace it with a much more dynamic background. This compositing technique is what I call 'impossible depth of field' because the 200mm focal length I used for the birds would never give me this much DOF such that the clouds were sharp. Only by combining two images in post-processing could create this much depth of focus. My settings were 1/4000, f/2.8, and 250 ISO. I used a 70-200mm lens for the shot. Note I chose a sky background that made sense in terms of matching the diffused light on the birds.