Smart filtering means that you can readjust the settings of a filter without undoing previous operations, reopening the original image or creating a new layer. It currently only works in Photoshop CS3 and higher.
Before you can apply NoiseControl as a smart filter, you have to turn the current background image or layer into a smart object. You do that by choosing from the menu Filter > Convert for Smart Filters or Layer > Smart Objects > Convert to Smart Object.
After you applied NoiseControl by clicking OK on its dialog, you see a NoiseControl item on the Layers menu.
To readjust the applied NoiseControl settings, double click the NoiseControl item in the Layers menu. You can also deactivate the NoiseControl effect by clicking on the eye icon left of it. To adjust the opacity and blend mode of the effect click on the icon with the two sliders on the right hand side of the NoiseControl item.