In the old days, within Photoshop, Contrast and Brightness were looked down upon because there were a linear correction. IOW, you shifted all tones in one direction. In modern versions of Photoshop, that isn’t the case unless you click on the “use legacy” check box. But as Jeff points out, this is all vastly different in LR anyway. So any comments about Contrast from old time Photoshop users doesn’t apply in LR/ACR and probably doesn’t apply in Photoshop much either, unless you have the legacy check box on. And, it can be useful to use the legacy behavior from time to time, especially on masks/alpha channels.