Should I avoid creating multiple variables when programming a shader?

I'm starting to learn Shaders now (HLSL, GLSL) and I saw a lot of tutorials where there weren't many variables created and that made reading harder. I was wondering if the creation of new variables affect the performance of the shader.

So, for example (in CG):

Is this

    inline float alphaForPos(float4 pos, float4 nearVertex){
            return (1.0/_FogMaxRadius)*clamp(_FogRadius - max(length(pos.z - nearVertex.z),length(pos.x - nearVertex.x)), 0.0, _FogRadius)/_FogRadius;
    }

Faster than this?

    inline float alphaForPos(float4 pos, float4 nearVertex){
        float distX = length(pos.x - nearVertex.x);
        float distZ = length(pos.z - nearVertex.z);
        float alpha = 0.0;
        alpha = _FogRadius - max(distZ,distX);
        alpha = clamp(alpha, 0.0, _FogRadius);
            return (1.0/_FogMaxRadius)*alpha/_FogRadius;
    }