"Live Preview" means that you can see what your color set is going to look like as you are programming it. This can really help save you time and having to re-do your programming by showing you exactly what you're programming as you do it.
While in the process of selecting a color to program, you can Live Preview by simply waving the Glove Light around. This will show you the color you are considering selecting combined with the colors you have already selected.
You will also see a Live Preview when you are selecting colors on the EmazingLights App. Simply turn the Smart Hub while you are working and hit the Refresh icon in the top right of the mode editing screen.