Viral marketing is a way to use social media to make awareness to the brand they are trying to promote. Social media influencers use viral marketing to promote ads on their brands to gain revenue. The ads will also sponsor the platform for them to promote the product in return will pay the influencer for promotion. YouTube is a wide supporter of doing ad revenue and even use partnerships with their users to put ads on the videos. The more ads and attention a video gets, the more money the user receives for their video.
Google has been using formulas and equations to configure what the best ads would be to pop up depending on the user. When using google apps and products, such as Google Chrome, they can go into your search history and understand the products you are browsing the most. Thus, no matter what website you are using, the ads will be geared toward what you look at the most.
In my opinion, especially with YouTube, I think ads are okay to have during the videos because it gives the producer a chance to make a living off their creative content. The only downfall would be that sometimes it can become too much. Too many ads can turn a person away from watching videos.