Each method extracts different compounds that are all related to the taste and effectiveness of tea and herbs.  Tannins, for example, give tea its dark color and is also a bitter component and is naturally found in tea.  Every time you have a green tea that is yellow/brownish, its because its been over steeped and too much caffeine and tannins have been extracted.  Caffeine is less soluble at lower water temperatures and using cold brewing can effectively reduce the amount of caffeine in your beverage and raise the natural sweetness of tea and tisanes that have a high amount of amino acids.  

Cold Brewed:  Add 3-4 Tablespoons of tea to a one liter pitcher. Add room temperature filtered or bottle water and stir to make sure everything gets immersed into the water.  Cover and refridgerate for at least 2-3 hours or overnight.  If you have a second pitcher you can strain the liquid to it and reuse the same leaves again for a second brewing.

Chilled:  Add 2-3 tablespoons of tea to an 8-10oz teapot.  Simmer water (195F), remove heat, and let rest for a few minutes.  Add water to teapot and steep for 30s and pour into a heat resistant pitcher.  Repeat two more times.  Let hot liquid cool for about 30min.  Cover and refrigerate for about 2-3 hours.  

Iced:  Add 2-3 tablespoons of tea to an 8-10oz teapot.  Simmer water (195F), remove heat, and let rest for a few minutes.  Add water to teapot and steep for 2min and then pour over two large glasses filled with ice.