OK, I'm a NOOB to diving, so I will preface this by saying that "I don't even know all of the things that I don't know yet"....
However, I personally live my life in accordance to two philosophies....
#1 - "Murphy has a law for a reason." Chyte happens, and with some people, quite often. And since I know this, I want to have all of my bases covered because Murphy likes to hang out at my heels quite often. I want to know how to do a CESA. Mostly because as a new diver, I don't know how fast or how slow I'm ascending, nor do I know (for fact) that a lung-full of air can get me to the surface if need be without actually performing this task. I know that I know absolutely nothing, and I readily admit it. Oh, my instructor can tell me something all day long, but I like to pretend I'm from Missouri - show me, prove it to me. This is how I learn, period. Nothing with me is taken on strict faith. And since I don't have gills, nor can I ever COMPLETELY depend on ANYONE else to be there when needed, I want to know how I can save my own skin & do so as safely as possible.
#2 - "When you know better, you do better." I know that I know nothing at this point as I've been certified OW for a whopping 5 days. But I do know that you have to learn how to crawl before you learn how to walk. Once you learn how to walk, there is little to no use for crawling anymore. But that doesn't mean you didn't NEED to learn how to do it, nor do you forget how to do so. I'm at the crawling stage of diving right now, which means that I'm learning how to control my bouyancy, my speed, my depth, everything. Tis far better CESA to be ingrained into my mind at this point, IMHO, than for me to freak out and drown or die because I'm a moronic NOOB and screwed up somehow. Once I learn to control my bouyancy, breathing, speed, etc there may be little or no use for a CESA in my diving future. Until then, I want a back up plan (for whatever reason), because I want to come home to my family at the end of dive...and not in a body bag.