Digital advertising has grown in waves with display, email, affiliate and search engine marketing being the major channels in the first wave. Then as the web, consumer behavior, and technology evolved, these channels were joined in a second wave by video, mobile, content, and social media marketing.
In a channel like paid search, even though Google dominates in most markets, the value proposition and method to market itself differs little to the other search engines like Bing, Baidu, and Yandex. Social media marketing has historically comprised of marketing on platform channels like Facebook, Twitter, LinkedIn, Pinterest, and Tumblr where most or all of the content has been user generated.
So unlike search engines where the form, function, and advertising opportunity is largely the same, the various social channels differ tremendously in their use cases, content, engagement, and advertising opportunities. Thus their value to a business and the overall marketing and sales funnel differs greatly both at the platform and vertical level.
While Facebook is clearly the largest player in town, a lot of agencies and advertisers would traditionally start from the concept of a social media budget and then allocate accordingly across the channels they chose to invest in usually with the largest portion going to Facebook. In this structure, the team and team leader would then be answerable for the performance of social media.