There's a lot that goes on behind the scenes. You need sales people to sell ads, designers to build out the creatives (assuming the company you sold ads for do

There's a lot that goes on behind the scenes. You need sales people to sell ads, designers to build out the creatives (assuming the company you sold ads for doesn't have media that fits with your platform). Then you need account executives to manage the account. Then you need a billing department that collects the money. Then you need engineering to build out your ad serving abilities. For IT you have the core that builds what some here have called a "shitty" UI. Then you have people working on all kinds of invisible things like developer tools to support releases. People working on recommendation engines. People working on instrumenting data and metrics for business analysts. Then you have people who hand-curate music for each of the markets and local tastes that Spotify operates in. Then you need people to manage these people... Etc.