In a candidate's market, even the best companies need a strong employment brand to win the war for talent. Just as a product brand is defined by the customer experience, your employment brand is defined by the employee experience at your company.
Most visitors to your website may not be actively looking for a job but would be open to new opportunities. A great employment brand works in the background to keep the career opportunities at your company top of mind for all website visitors, slowly converting them from visitors to candidates or referrers. Do they come away feeling positive or neutral about your company? Can they easily find good reviews from your current employees online? If someone walked into a bar and said your company name out loud, would people immediately think of it as a place to grow their career or "just some company"?. There a few ways to easily boost your credibility with (especially) passive job seekers.
Good companies are marked by employees who speak positively about their experience. Teammates who are vocal about positive experiences create credibility for your employment brand message and are more likely to refer their friends for openings at the company.
Great employment brands are marked by something magical - even people who aren't employees start referring their friends to your company, simply because they have heard so many positive things about it. Don't sleep on external referrals when it comes to employment branding.