Why do we need Advertisements?

It may seem provocative and counterintuitive but the reality is that advertising serves many human needs. The fact the notion of advertising exists and it's so prevalent in the world is not a sign of the devil, but a sign that it's a industry that while having several significant downsides, is also essential for contemporary society. This is why ( in no order)

Advertising drives economic growth.

Without advertising is would not be possible to tell people about new products and services, innovation would grind to a halt and there would be remarkably few products around. It would be near impossible to innovate in a world where it's not possible to tell people efficiently about what you have done.
Maybe this seems a bit far fetched, but imagine how you would sell used items you don't want,, or a house, or find a flat to rent, if you can't use classified ads or craigslist.

Advertising helps people choose

People like having information to hand to be able to make informed decisions, people like the concepts of brands and buying into a belief system and not just a product. Rightly or wrongly, brands give people a sense of joy.

Advertising allows some business models to function.

Advertising is what allows TV, Magazines, Newspapers most of the internet to exist. Without advertising all these media would either be hugely expensive or simply not exist. Advertising also allows bus stops to look nicer, public transport to be subsidized and more.

Advertising allows us to express ourself.

The notion of branding is actually liked by people, people like to wear certain brands and use this to express themselves. In a world with no advertising, there can be no brands.

Advertising in some ways (oddly) is good for the environment

makes people spend money on intangible things and not simply more and is therefore more environmentally friendly than we may think.
Tom Goodwin