HSL Secondary VS Masking

HSL is still masking  ... it's just another toolset to create a mask prior to applying very controlled corrections. It is especially useful when 2 or more of the key types are involved. Often you do get better results turning off one or two of the key sections , H, S, or L.

It does work across the entire image unless of course you apply a mask before that instance of Lumetri in the ECP, to only allow it to affect one area.

And sometimes that is very necessary  ... apply a mask before the Lumetri instance to control area, then use the HSL key settings to affect certain things within that area.

You probably haven't realized that some of the new Curves tools are also at heart a masking operation. Selecting only the skin tones in Hue v. Hue, or the shadows in Sat v. Luma for example.

Use the tools that get you where you need to be quickest and with least damage to your pixels.

Neil