Does it work? I don't have any hard science to back it up, but I've worked with many brands who see a ridiculous return on it (despite paying between $50-$2000 per post). It doesn't work for every brand though.
I'm a dev, I work in the industry (I run a startup in this space, check profile if interested), and I consider myself minimalist and not materialistic. Yet when it came time to purchase my first watch, I went with a nice, minimalist looking brand I'd seen advertised on IG constantly. Same with when I needed to buy a new set of t-shirts.
We constantly ask for recommendations on HN and accept them without verifying who the poster is or if they have ulterior motives. I've bought _so_ many books off of HN suggestions because I give the average poster a respectable amount of trust. It works the same in IG influencer marketing - those who follow a particular influencer grant the influencer a modicum of trust and are willing to trust their recommendations more than a banner, billboard, or magazine ad.