I'd like to enthusiastically support this too.
Closing tabs shouldn't be homework. I want to open tabs as I need them, and unless pinned, have them just close behind me after a time. In Arc, I used 12 hours, but some configuration would be nice. At no point should I need to manually go through my tabs, clicking a bunch of close buttons or Cmd-W...that's busy work, and it doesn't serve me.
I do not want them suspended, I want them closed (unless pinned of course)
Low power mode is also a nice option, but it's clearly oriented around power by suspending the tab. That's useful, , but it's a very different feature and fills a different need.