Our voices are a beautiful, natural instrument we carry everywhere with us, from the shower to lonely business trips to walks in the park. I've always had the desire to put it to work. Singing is also an ancient tradition of bringing melody and lyrics to people. For me it's not about singing like a soul or blues singer (ie Joe Cocker) but more like Chet Baker: get the notes right (pitch) and building them into elegant phrasing, which needs control of tempo and great diaphragm training. Music is undeniably great for your brain, which can include learning and memorizing a ton of lyrics, tempo and pitch. As an art also very appreciated by most people, who really feel grateful by a (good) vocal performance, sometimes more than by any other instrument. Hearing yourself improve and sing well gives a high dose of happiness and confidence builder.
It's also an excellent breathing and speaking exercise, which increases your ability to communicate effectively, projecting and modulating your voice effortlessly and making it easier to jump in into a conversation. Also gives your voice the stability to fend off your nerves or anxiety. For an introvert like me it's definitely a very effective tool, it makes me feel like "in the matrix" as far as speaking goes, as my brain thinks ahead of time or just in time, so my mind feels snappier. In other words, I feel like a more spontaneous person since I've started to sing.