What is the purpose of private job postings?

In some circumstances, outsourcers who might otherwise post a job at ProZ.com refrain from doing so because they don't want their search activity to be publicly visible (ex. to their clients or competitors). Private job postings allow outsourcers to make these job opportunities available to eligible service providers at ProZ.com. While this might decrease the number of job postings that are visible to any particular user, the goal is that it will increase the overall number of jobs passed through ProZ.com, and improve the relevance of job postings accessible to each provider.