First, you want to let the hiring manager have control of the interview, especially in the beginning. If you start off the first 10 minutes of a 30-minute interview with a monologue about the details of every job you’ve ever had, you lose the back-and-forth, give-and-take conversation that builds rapport, and it doesn’t allow the hiring manager to structure the interview the way they’re used to.
Second, what you say can hurt you. Let’s say that the advertised position listed several desired qualities such as team management, writing skills, technical chops, and graphic design. You’d be surprised at how often the posted job description can vary from the actual work -- the job listing might have been written by someone outside the department, or the goals of the group might have changed. If you spend 5 minutes talking about your extensive design experience, and it turns out that skill is only needed about 10% of the time, you’ll come off as a poor fit for the position.