This year, companies worldwide are expected to spend 1.08 trillion U.S. dollars on advertising. But the amount of value lost to humanity is about double that. Here is why: advertising actually works. Companies gain at least as much from it as they spend on it, or they wouldn't do it. Advertising works by manipulating people to make objectively bad decisions. To buy stuff they don't need or buy stuff at elevated prices keeping up monopoly like pricing. How much useless stuff? How much higher prices? Well at least another $1.08 trillion worth of course, or companies would spend less on advertising. Basically people need to work to make the ad, that makes you buy useless shit and then people need to work to make the superfluous product and/or to afford an overpriced one.
And this is just advertising, not general marketing, branding and public relations. People like to think, that ads are just annoying or that they work on everyone else but them, but the truth is, they work on all of us and cost us a lot of money. Not to mention the often cited ideological effects of making us feel unhappy, inadequate, fearful, sad, sexualized, pressed into gender norms and social classes and so on.
So the material loss to humanity is about $2,160,000,000,000 this year. Poverty, hunger, climate change, take your pick - oh wait, with this kind of money you wouldn't have to choose, just end them all and still have a lot left over. An alien race looking on earth from the outside might be amazed at how we spend so much energy, time and effort, just to dull our own minds.
From a Marxist perspective, advertising is driven by the capitalists urge to avoid what they hate most (at least in their own sector, not necessarily for their suppliers): fair competition. By manipulating demand with advertising, they get closer to monopoly prices. That's why, we can't realistically hope to get rid of advertising within capitalism. It's part of the ideological manifestation of the tendency of capital to form monopolies.