Don’t worry about it. you are just getting the discussion started. So Texel Density example is good one. that got me thinking how it should be used. 
I am very familiar with Texture Atlas… You could say I am an expert in modeling and texturing using node editor in Blender. BUT i do not have enough knowledge to know more about texturing and how it should be setup for gaming.
Option A: What if there are 3 objects that have: the body and 2 wheels of a vehicles. If you unwrapped them that they have their own UV map separated from each other. That would take up lot of memory usage because there are 3 texture image, right?
Option B: Same with 3 Objects, Texture Atlas can be used to unwrapping all of 3 objects in the same UV map’s space. the islands of wheels are not in the same position because they have texture where they are dirt, rusty or old. So 2 wheels are separated. The texture size can be a little bigger than Option A. This can save a lot of memory usage because there is only one texture image? Right?