I feel ya, Experience is almost always better than advice.
Youre still lighting up the same amount of pixels regardless of resolution. The only way you would see any battery increase is if the phones main purpose is gaming and videos 24/7. But for an average (or even some power users) there is no benefit.
And yes they kind of did, most samsung phones in verizon or best buy that loop a demo video showcasing and explaining features have a good 1 1/2 minute clip telling you why it will save hours of battery over time without sacrificing visual appeal.
You can do a little research if you would like, start with reviews of samsungs implementation and if you still want to try it then you can do it via terminal emulator. The commands would be.....
"su" (gives root to terminal)
"wm size 1080x1920" (This changes the resolution, you may want to play with values)
"wm density 420" (This will change the dpi to make up for the lower res, and will help visual items retain their correct ratio)
DO NOT RUN THESE COMMANDS without understanding what they do, or that inputting a wrong resolution or dpi may damage your device or make it unusable. Search and search. Make sure your device can support the resolution and DPI values you want.
As always, backup before modifying any system values like this. Worst case scenario, you can reset your device back to stock and restore all your data