Do I need advertising?
Not all advertising is created equal. Not all promotions are created equal. Even if you're not doing traditional "advertising," if people are buying your product then they likely ran across it or heard it from somewhere.
Short answer: People will always need to learn of your product in order to buy it.
Longer answer: Your message (discovered through your marketing or advertising) needs to speak to your audience and drive a change or it's not worth paying for. If you're not interested in traditional advertising and media spend, look into ways to market your product through channels you own or develop something worth talking about, like Tesla.
Tesla describes their method of marketing for their newest model "the anti-sell." However, they are already an established name brand and receive plenty of free press even if they don't advertise. Unfortunately, not every brand receives this kind of love from publications.
While you probably don't need to a launch a brand new TV commercial for your product (like Kobe), people do need to hear about it somehow so they can begin interacting with your brand and product. Sometimes, these advertising efforts can be clever enough to gain attention without breaking the bank in media placement. Not all spending to drive awareness requires a large budget and it can be the more interesting ploys that gain attention over the ones flashing dollar signs.
One of my favorite examples of great (and cheap) marketing is from Cards Against Humanity. Instead of airing a Super Bowl ad, they made a fake one.