While it sounds ridiculous, there is a reasoning for this even nowadays:

Any periodic activity with a rate faster than one minute incurs the scrutiny of the Windows performance team, because periodic activity prevents the CPU from entering a low-power state. Updating the seconds in the taskbar clock is not essential to the user interface, unlike telling the user where their typing is going to go, or making sure a video plays smoothly. And the recommendation is that inessential periodic timers have a minimum period of one minute, and they should enable timer coalescing to minimize system wake-ups.

Found 1 test that seems to confirm battery life is slightly worse (2%) with seconds enabled. But this is true only when nothing is going on on screen. If you would actually work on PC, I imagine difference would be practically nonexistent.

All that said, I use seconds on my private and work PC. Was pissed when MS initially removed this as an option.

The only time that would make a difference is if you're staring at a blank page and the only thing causing the screen to update is the clock. Theoretically the GPU could go completely to sleep, except for having to draw the updated clock every second.

But there's a reason battery life is commonly measured as "hours of video playback". If the laptop's not actually doing anything you may as well turn it off and get weeks of battery life.

My god. It really does!

Oh no! I left notepad.exe open. That cursor was flashing on and off for hours! I'm sorry everyone!