At almost every session or wedding my clients ask me "What's that thing around your neck?". It's an Expodisc! I guess it doesn't look like your typical photographer tool. I rarely carry a reflector and shoot all outdoor portraits with natural light so I travel pretty light. Each time I move to a new location or if the lighting changes drastically, I pop this baby on the end of my lens and stand where my subject will be. I point it to where I will be standing and it does two things. First, it measures the colors and sets an accurate white balance. If I do not use this tool, then images come out of my camera looking flat and gray. It requires some tweaking when I am editing to get colors correct so this saves me tons of time during post processing! Second, it also measures light somewhat more accurately than the meter in my camera and will help me set a proper exposure so that my photos are not too dark or too bright.
If you look carefully you can see my gross neck sweat stains on the strap thing. Yuck.
Here are a few of examples of photos using the Expodisc vs the Auto White Balance feature on my camera. The difference is subtle, but I love the results!
White balance is one of those things that is entirely a matter of personal preference. Some people may prefer the cooler settings of the auto feature and that's perfectly OK! I personally prefer warm skin tones which is why I utilize this tool a lot.