The best interviewers get the most out of their guests (more than if the guest were to give a monologue). They refrain from driving the show and instead let the show develop naturally from the guest's remarks.
The worst interviewers impose their own personalities onto the guest and the show and make a concerted effort to steer the direction of the show as they will. The guest is hampered from expressing the most interesting parts of his character and his arguments, as critical points are often diverted rather than expanded upon by the interviewer.
The first and most memorable encouter I had with the latter was in watching various MSNBC shows in the summer of 2005. The interviewer kept putting words into the guests mouths and asking questions where the desired answer was obvious. The show host insistently imposed her persona onto the direction of the show and stifled the guests. It was disgraceful and frustrating to watch.
I recently came across an even more elucidating example of this problem. . The first video is with a host who imposes his persona onto the guest. The latter is with a host who refrains from doing so and does a much better job at drawing insights from the guest. The guests are Richard Stallman and Steve Wozniak, respectively.
Pretty big difference (though admittedly the second interviewer is just plain "better" so maybe this isn't an entirely fair comparison, but the difference in viewing experience is dramatic).
(The only exception might be shows where it's understood that the strong personality of the host(s) is a vital part of the show's value to the viewers. ex: Pardon the Interruption on ESPN)
Addendum: This is likely relevant in an applicant interview setting as well for any company.