I've done a multi-day trip with just rear panniers and a handlebar bag, some overnighters with bikepacking bags, and others with just front panniers/saddlebag. I'm an oddball, I suppose, because I found the rear panniers to be annoying.
The idea behind the bikepacking setup is that you put your heavy stuff in the frame bag, keeping the weight centered on the bike, and it actually keeps the bike handling pretty normally. The stuff on his mini front rack is a sleeping kit and a tent. It's mostly just bulky, and probably weighs less than a conventional bracket mounted handlebar bag and the hardware for it, plus all of the junk, camera, and granola bars that you'll inevitably shove into that handlebar bag.
For lightweight offroad travel, which is what was intended on the trip that that photo is from, having that rackless setup makes your bike a lot easier to throw around or over obstacles, and push up bad sections of road or trail, and in my personal experience with this sort of setup, carry through hotel lobbies, and up or down stairs.
I think of the weight as a bit of a percentage thing. If you've carrying 50 pounds of gear, 4 pounds of racks and pannier hardware doesn't make a difference. But if you're going lightweight enough to fit in a bikepacking sort of setup, then 4 pounds of rack and pannier hardware is a much greater portion of your load.