In addition to my instrumental skills, I am also a professional vocalist. I have been in numerous vocal classes and private lessons through the years, as well as performing in choirs, stage plays, restaurants, weddings, and parties. I believe any instrumentalist can benefit from vocal skills, as it's an instrument that you carry with you wherever you go!
    People who learn to match pitch with their voice tend to "internalize" notes and musical concepts in a way that people who are strictly instrumentalists cannot. Also, it's the kind of instrument that the majority of people identify with the most when they see a musician performing. And let's face it- usually it's the singer who gets the spotlight the most!
    Most anyone who can sing "happy birthday" is able to develop their voice into a skill that they can be proud of. The hardest parts are psychological- such as getting over the "you have to be born with it" myth. You might notice that I refer to the voice as an "instrument", and I recommend you do the same- just because you have a good speaking voice doesn't mean singing will come easily to you. In the same way,  just because I might use the back of my guitar as a desk to bear down on doesn't make me a good guitar player. The voice is an instrument that you have to practice at just like any other instrument, and has about the same learning curve- some things are difficult, others have a quick payoff, but it's a journey all the same that takes some time to get some skill at.
   If you have ever seen yourself singing onstage with a rock band, or performing a powerful love song, singing in a play or production, or even just doing better at karaoke, you should develop your singing skills in vocal lessons!