It is helpful sometimes to render the image with each one of your lights one at a time so you can understand better what each of the lights is doing. The first image show the scene lit by only the key, fill and accent lights individually.
The key light provides good lighting, but very deep shadows. This makes for an artistic kind of lighting that can sometimes be used for edgy portraits.
Just the fill light produces very flat lighting, which on it own is not very attractive. This is similar to the type of unflattering lighting you get with on camera flash. The shadows you get from the off axis key light make the image look more 3 dimensional and pleasing, but just the key light produces shadows that are too deep for most people’s preference. Combining the key and fill gives nice 3 dimensional lighting
Just the accent light is only illuminating the back edges of the arms and face.
The second image shows the combination of the key and fill, and the combination of all three lights. This shows the subtle change the back light makes in the image.