It works well for the viewer if the content lends itself to sponsorships - your friend's example is a perfect one, he has a cooking show, needs cooking equipmen

It works well for the viewer if the content lends itself to sponsorships - your friend's example is a perfect one, he has a cooking show, needs cooking equipment and the sponsors provide it - win-win! But this model doesn't apply to every channel. If I'm on a science/physics channel, I'd tolerate scientific/test equipment sponsors but that's rarely what we see (turns out most quality goods sell fine without polluting YouTube videos), so instead you get VPNs, crappy Chinese earbuds, website builders, etc.