Mark, Santora has already stated
I am not sure I follow, Joyce. If you didn't do the CA, then why would you need "the obsolescence?"
What SS appears to be saying is that we just do not do the cost approach, and that we will then never need to worry ourselves with issues of functional obsolescence, external obsolescence, EI, physical depreciation, RCN, effective age REL, and all of that stuff that goes along with the cost approach. Think of the money the publishers could save if they just removed all of that stuff from the Books and manuals!
Seriously, Mark, you have run into a member who has his search engine set to the words "cost Approach" in this forum, and he pounces in with this constant anti CA rhetoric over and over and over. Unfortunately it, and he, sidetrack every thread that starts to this same all to familiar conclusion...
For years now he keeps saying he is going to write a book exposing the cost approach, and suggesting eliminating it from use. I guess the publishers are just not knocking down his door, yet. (can't imagine why?)
Mark, you will even find resistance to the concept of EI here. It didn't appear in the major appraisal texts as an entity until the '80s I believe. However, call it what you want, if the well supported and properly completed cost approach suggests a value indication significantly higher or lower that a sales comparison approach, SOMETHING is amiss. Could be EI, functional, external, but at least it opens our eyes to the discrepancy (AND that discrepincy COULD be in the Sales Comparison Approach!). For that reason alone, the CA is valuable.