A song needs to grab the listener emotionally to have an impact. Part of that emotional response is caused by frequency. If the song is exciting, because it reaches a frequency where we react as listeners, you as the singer is giving the audience what it needs.
How do you find the right key?
The dramatic part of the melody, usually the chorus, has to have pitches in and just above your first bridge. For women, the first bridge is A, Bb, B and C. Therefore we find choruses often going to a C#, D or sometimes Eb. For men, the first bridge is E F, F# and G. Therefore we often hear chorus notes on G and Ab.
If you do not mix into those pitches just mentioned, you will get hoarse and develop nodules on your vocal cords. If you put your key for the melody to go below these notes, but still choose to have a tessatura in the bridge, for instance on a Bb or a C, you still will get hoarse if you don't mix.
You are also now in a territory where it starts to feel boring for the listener. If you go below in a very comfortable range, it will feel like you are trapped in a box and don't share your range. You may not think you have it but the listener hears - and misses - what you could have given them, had you only mixed.