I love my light meter.
I'll give a quick example.
Suppose you want to set up a reverse key interview:
Notice my 1k (key) is behind the subject and the 500 (fill) is in front. The bounce is to both flag the light from the huge office window and to bounce a little bit of the fill around the face to give an evenness to the lighting. If my shadows were not strong enough, I'd use black.
Here is my front (fill) meter reading
Here is my rear (key) meter reading
That's a good ratio for what I'm after, if you wanted a stronger ratio, you could dial back the fill, or dial up the key. Here is the result, featuring yours truly:
Now, what you can't see in this iphone pic is that the key side of my face is actually properly exposed (I set the aperture at f4) The iPhone boosted the exposure making it look like the key was too bright.
I set the lights with the meter, then turned on the camera and took this. No wasted time using a histogram to try to interpret what my key f stop should be. No guessing that the LCD is showing me accurate luminance.
Use a meter! (When you can.)