You are correct that site images are the default for stacks4 running under RW8.
You do lose the ability to do some of the image manipulations that you can do with the old image stack. You can still use the old ”image” stack if you want some of those edits. However, you’ll trade-off the benefits like performance outlined in the video.
You can check out the videos here on the new major features of stacks 4. Feature #4 is on site images.