As a journalist, non-fiction writer in a niche topic, or a generalist, your work can benefit greatly by interviewing others and using their knowledge and quotes in your articles. By asking questions and listening to the answers, you as a writer are acquiring original source information that is absolutely unique no matter how many other writers are working on the same topic. By going directly to the source, your article benefits from increased credibility.
A thousand people can write about the latest study linking the excessive eating of ice cream and unprecendented gains in longevity by using the original published research paper as a primary source. All one thousand of those writers will have access to the same facts, the same researcher comments, and will all see that original source material worded exactly the same way. Many of their reports, even those found at major outlets like Reuters, AP, and Yahoo! will be very, very similar in content and tone. By talking to the lead researcher directly, however, you can follow any angle of questioning that you think is interesting. You'll get original quotes that are different from those that appear in every other published report on the subject and you'll almost certainly get facts and insights to which no other writer has access.
In other words, you'll be able to turn out a better article than anyone who relied only on material that is presented in identical fashion to everyone. That's not to say good, or even great articles can't be written without original interview material. They are every day. It is ultimately a question of the writer's imagination, creativity, skill with words, discipline and experience that dictate the quality of any article. Starting out with higher quality, more unique source material such as an original interview, however, gives the artist a bigger pallette from which to fill the empty canvas.
As if that weren't enough of a reward, you may find yourself earning higher upfront payments for these highly original articles as well.
For some, finding the right people to interview can be difficult, though. On one of my other blogs (Interviews with Experts), I am launching into a series of posts about identifying, contacting and securing interviews with original sources from many different walks of life from the everyday person, to the knowedgeable expert, to the celebrity.