It has other uses as well. If you look into the application menu on the phone, there should be an app titled s pen user guide. Click on that and it should explain some of the s pen basics as well as how the button is used in some instances.
I have the Wacom bamboo paper app on my note 2 and the button works to toggle between ink and erase. Kind of a rapid switch if needed to make corrections.
Most button functions work in samsung's touchwiz sandbox due to the os integration, but in their marketplace, there are a few other apps like games that are s pen optimized as well.
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