PR given by Corez Some pretty old articles I wrote for the magazine at ProVision, hope you guys learn something from them.
Photo Filter, Hue/Saturation, Brightness/Contrast; all of these form together the ultimate tool's to enhance your photo's. But, there's two ways to use them. You can either do it via Image > Adjustment or Layer > New Adjustment Layer. The key difference between them is that the first one only effects the current layer that you are on. The latter effects ALL the layers below the Adjustment layer.
The safest way of working with these tools is by doing the "Layer > New Adjustment Layer" method, because if you want to change the settings (add less contrast to your photo for example) then all you need to do is double click on the Adjustment layer and wha-la there you have it, a window pops-up and you can easily adjust it to your new desired needs.
The other method can also be adjusted later on if you want to, but you can't always do this because once you close the document (save as .psd, though), all the history for the files are lost so you can't Undo. You'd have to play around with your tools until you get what you desire or, if you were smart when you saved the file, open the original photo.
Try playing around with both method's and you'll probably discover that there are more differences between these two methods.