Due to it being compared with advertising, PR is maybe the least understood of all marketing tools. The basis of PR includes using intermediaries to communicate with your audience and influence them. Those intermediaries may be industry spokespersons, stock analysts, investors, trend setters, industry analysts, customers, employees, and even the electronic and print media. Typically your brand has very little control over those influencers, or intermediaries, which will make public relations so difficult.
PR is messy
Advertising, on the other hand, provides you that control. You won't just get to create your organisation's messages, match them with a supporting graphic, then place them where you desire your audience to read them and as you desire them to read them. Plus, you'll pay for that control. In order to get individuals to hear you, you must persuade the press that your brand, its services or products are worth their time to consider writing about.
PR is personal
You might have demographics for your audience in advertising. You might even have performed focus groups and market research to pin down their necessities. However, as individuals the audience remains mainly anonymous to you. You'll communicate to them more as a circle that shares common interests, instead of as individuals. Advertising, by its nature, includes a mass communication.
PR builds up credibility
Public relations boosts an organisation's credibility, because it'll operate through numerous trusted intermediaries. Plus, these intermediaries communicate to a certain audience which looks to them to filter out all nonsense. If messages are chosen to be communicated, they'll gain credibility due to the intermediaries' credibility.
PR is precise
With advertising, it's possible to calculate the responses and audience impact which you have. It is similar to a controlled experiment which is being done repeatedly. Public relations is less predictable due to you having to get the intermediary to comprehend your important message points and reiterate them in his/her messages. It means cautiously aligning them with an intermediary's messages. It'll mean knowing his needs and your audience's needs and where your brand and its messages fit within that environment.
PR is based on relationships
Great public relations means setting up ongoing relationships with many important members of the press (and therefore their readers) and knowing how your brand may become an excellent data source for the influential.
PR is not free advertising
It is a time consuming and labor intensive effort. It'll mean opportunistically thinking and evaluating 'what is news worthy' concerning your brand with a keen eye. If your business is able to do this, PR may help it look more influential, bigger, and more important than it may otherwise be.