Sometimes API calls can be a meaningful expense, depending on what you're using and how. Weird resource usage can sometimes be a problem if you don't watch it.

Sometimes API calls can be a meaningful expense, depending on what you're using and how. Weird resource usage can sometimes be a problem if you don't watch it. Infinite recursive operations, brute-force algorithms being called over and over per user, stuff like that. Advertising will take whatever you throw at it. Personnel costs are likely to be the dominant factor for most web projects until you start talking serious, serious scale.