Jaime Lee Curtis has a classic one in Halloween. The frightened voice, though it may be quiet, drips with emotion and fear. It's the perfect one to convey the feelings that may be only better expressed through a scream.
Classic horror movies use these voices perfectly A frightened voice expresses true fear, whether it's someone hiding in a dark spot in the house or whispering in a call to 911. When your character is afraid, the frightened voice expresses this, and we, the audience, feel the fear that's emanated, no matter the circumstance.
Audiences love to be afraid. When you are in the process of scaring your audience, use a frightened voice. They'll love it. They'll feel the fear, and in an audio piece, they can imagine grand, horrifying things heading their way. We want to help that frightened character, but often we are too afraid to move ourselves when we hear it. We know what lingers in the dark. In other words, it's a great voice for your audiences that love to be afraid.
The frightened voice is often a strained whisper. Fear drips from it, and its hushed tones only emphasize that fear. It can also be higher pitched when face to face with the fear itself. The voice may also be shaky and trembling to convey even more fear.
The magic of voice work is conveying emotion without having to describe it. No one wants to hear a description of how afraid a character is when the character herself can tell us through her voice. An effective voice artist will get this across to the audience, and they can be frightened together.