So i use this projector for about 70 percent movies/tv and 30 percent video games
If your room is dark enough, i see no problem leaving it on eco mode. The colors are more true to life and the picture still looks great. Lampsave tries to do dim to less dim but the process is clunky.
You can keep in SmartEco for a best of both worlds but the changing brightness can be pretty distracting as well.
I do encounter from time to time a bit of flickering in the highlights when in eco mode or lampsave that is separate from the dimming. Usually switching to Normal or SmartEco for a bit helps when it happens but it can be pretty annoying.