The display can slow the display to 1hz on static images and it helps a lot with battery (variable refresh). For example you on macrumors and reading and not moving the screen. It slows it to 1hz. Not 120hz.
On 60hz it stays at 60 whether your moving the screenings or its a static page.
The Apple watch has this same technology and how it optimizes the display with small battery. Pretty cool tech. The series ten can now change the display to 1hz on the aod when the screen is “down” or wrist is not raise. So the minute hand refreshes 1 second at a time.
ok so then the battery life depends more on the kind of activity you're doing than on the screen time itself. like with gaming etc the 120hz would consume more power. Well anyway for me it doesn't matter so much as the 16 gets me through the day easily and I don't miss the 120hz (though I noticed the difference when I was looking at a pro model in the shop, it's not a must-have for me )