Lock Transparency vs Mask Layer Contents

Hmm, they are similar in result and I'm having a hard time trying to explain why I would use one over the other. 

Lock transparency - this is where you have your shape or maybe an outline and you want to fill it or change its colour. Locking transparency means the fill won't spread over the whole layer and also that you can accidentally draw elsewhere on the layer. For me, locking transparency is something I use when I have drawn something exactly as I want it and don't want it to change in shape. 

Mask layer - it's non-destructive in that any layer contents are not removed they're just hidden or revealed depending on the mask. I'd use a mask for something like texture that I've painted over a design. where perhaps I want it more obvious in one area but fading out in another area. Lock transparency wouldn't work here because you wouldn't be able to fade parts of the texture. 

I doubt this has been of any help at all 😂