When a software upgrade is done existing users frequently just “jump in” to the new version without much thought. I did a quick review (too quick!) of the new features and in doing so I missed something “BIG” that changed with RW8. It could be called “live preview” but that hints of a live website so I guess it could be called “real time preview.”
The Device Simulator could actually be called “Active real time device sized and/or custom sized preview window(s).”
I highly recommend EVERYONE watch the COMPLETE Device Simulator video which is found on the RW8 page. (Click “See it in Action”)
I also recommend this “answer” video that Isiah quickly made in regard to my mis-understanding of how “Preview” works in the new RW8. Special Thanks to @Isaiah for making this. If you are a long time RW user you this may seem “old stuff” but RW8 is moving upon new ground and Stacks is moving right along in support.