I thought I read something on BA about this and just did a search and came up empty, so I’ll ask the question.
What is the technical difference between an add shader vs. a mix shader?
Technically a mix shader will layer your shaders based on a factor, while an add shader will give you the sum of the input shaders (i.e. 1 + 1 = 2)
Guess i’m lucky then since G on “blender cycles Add vs Mix” brings me this which answers most of the thing using a bit of a math what could be considered technical here.
Ok… I suspected as much but thought that was too simple. 
Now I’m confused about some of the node setups I’ve seen others use that use add instead of mix. When I use mix in those cases the finished material/texture was much nicer looking…
Generally you want to use Mix only, not Add - Add might lead to “unrealistic” render results in a way that “registered” light is larger in value than “incoming” light from light sources in scene. There are some corner cases when you need Add to compensate for some node operations before, but these are rare.
Another is that Mix allows for mixing using some rule (reflections on bent surfaces e.g.) which can be changed, while Add does not allow for that.