Research is important for any job in any career. But for a PR practitioner, research can make or break a campaign or pitch. Practitioners spend weeks, months, or even years putting together a campaign for their client, and if they wrote the entire campaign without researching anything about it then it will most likely fail. When making a campaign you have to research the client themselves, the audience, the location, the business, the surrounding areas, numbers, etc. and not researching these things can be disastrous for the firm, campaign, and client.
If you do not have research to back up a claim then the claim would not be taken seriously and all credibility would be lost. A PR practitioner relies on credibility with clients so their good word will bring in more clients and revenue.