If a candidate has to choose between two similar vacancies, one at a company he/she already knows, the other vacancy at an unknown organization, the candidate will usually go for the already known company. In a nutshell, this is the philosophy behind
employer branding. A form of long-term marketing that focuses on promoting an employer image to potential candidates.
By promoting brand awareness and marketing your organization as an attractive employer, candidates will find their way to your organization (and vacancies) more quickly in the long term. Think in this context, for example, of Google or KLM, which, due to their attractive employer image, always have talented candidates to fill vacancies.