Many people start singing at a level they are comfortable with in the house, but that doesn't neccesarily translate to singing in public. What I call, "bedroom singers." For every song you sing there is an optimim key, but you have to find it. Just because you can sing a song in "C" doesn't mean that's the best key for your voice. It may be or even higher still in E. This is especially true if you have never sang with a band, and I mean a "loud" band, where you need to project above the music to be heard. I hear so many singers at sessiosn who I think could be a lot better if they just sang in a higher key. Of course you can go too far the other way, which is why I mention the optimum key for your voice.