I don't think advertising for jobs is a zero-sum game, especially if the matching algorithm is good enough to match employers and employees that had no knowledge of each other before. If you are able to reduce those search frictions, you have created value. Several economic professors won the Nobel prize for their work in this area:
Well, those Nobel prizes are for a specific theory. In practice, in this case, you see developers looking to get problems solved (or solving problems), and getting distracted to look for another job. So even if you are removing market friction, there's a huge cost in people switching (or even getting distracted all the time). In my opinion, if people are looking for a job, they should go to a job-hunting website (even if it has lower-quality data about them).
Anyway, it would be nice to have the effects properly quantified.
Anyway, it would be nice to have the effects properly quantified.