Feedback might not be desired for speeches, but guitarists love it. Well, some do at any rate. Throwing some controlled feedback in a song can work wonders.
Here's some trivia. What was the first time feedback was intentionally used in a song? 1964 when the Beatles opened "I Feel Fine" with Paul McCartney's bass feedback. The Beatles claimed at the time that it was an accident, but it was done on purpose and may have actually launched a revolution. Feedback wasn't desirable until the Beatles used it and showed how effective it could be.