Came across this advice from PHOTOSHOP COLOR CORRECTION by Michael Kieran.
I thought it was interesting, especially for someone like me who, in the past, tried to learn Photoshop the DIY way by just clicking here and there to see what happens.
The reason is this: “Brightness / contrast will definitely, positively, certainly, undoubtedly throw away valuable tonal information from your images.”
eg, if increase brightness by +15, then any pixel with a brightness value of 240 and above will become the same colour, ie pure white, at 255. So you lose all the details in the highlight.
Adding contrast, according to the author, is even worse as it pushes out the highlights and shadows.
Author recommends using levels and curves to adjust instead.
So alamak, I have to revisit all my pixs and re-adjust them. Serves me right for trying to DIY.