Computational resources

Hi Kate,

Yes!

If you can use one Principled BSDF, using Mix Color (MixRGB) Nodes before the Principled, that will be 'cheaper' than using two (or more) Principled BSDF's and a Mix Shader.

There are however situations, where you want to mix different Shaders together (for instance for more control over individual components), but mixing Shaders is always more expensive and can even lead to problems, especially when using Eevee:

https://cgcookie.com/community/11391-industrial-environments-with-eevee-course-columns-turning-magenta-when-mixing-in-second-principled-bsdf

But I wouldn't worry that much, it's not like your computer is going to cough smoke or anything. The impact most probably wont be that noticeable, unless you have lots and lots of shaders. That said it's always a good idea to build shaders with resources in mind.