Clear up how expensive material instances really are?

Hi, as the title says i was wondering if someone could clear up just how expensive material instances really are?

My general understanding was that a “Master” material would take up 1 draw call per how many times its used and
material instances would be “combined” into a single draw call no matter how many were used in the world (like instanced static meshes).

When searching for how expensive Mat-Inst really were i read that if the Mat-Inst had unique parameter values then they would
each use 1 draw call similar to regular “non-inst” materials, so now i’m confused and there is no documentation on
material instance expense.

Any insight is appreciated.

there is quite some documentation available actually, and besides a simple google search, this answerhub is filled with identical questions, and identical answers.

any material and any instance on a mesh is one drawcall. so one mesh with three master materials is three drawcalls, one mesh with three instances is three drawcalls.

most of the information can be found here:

and additionally: Mastering Material Instances | Live Training | Unreal Engine - YouTube
Though I am not gonna bother linking the basic google/answerhub questions besides the answer of this one:
What is the difference in performance between MaterialInstace vs Material? - Rendering - Unreal Engine Forums

also, importantly is, creating one master material for all your walls, would mean you only need to create that material once and then instance it for others. this saves you lots and lots of time over the course of your project. and that can be worth a lot of money. (since time = money)