Well, "good enough" is relative...Let me say this...I think anything you can learn about nutrition and exercise science is not only going to be a plus for your clients, but its going to benefit you as well...
I was lucky enough to train with an IFBB Pro for years while I learned the trade...after I started getting a good enough reputation where guys came to me for certain things, it kinda snowballed....he would send me his overflow because I was the only one he trusted and I garnered a reputation amongst two groups of people....bodybuilders, and fighters/pro wrestlers....one step leads to the next and sometime years ago, I was fortunate enough to meet and become friends with Patrick Arnold...what I have learned from his has been insane, and I have furthered my knowledge because of that....I have trained many pro wrestlers, ufc fighters, and countless bodybuilders...guess what type of cert I have? Some piece of crap that I got online for little of nothing...why would I do that and risk my reputation with my clients over a shitty cert? Because they know me, know what I have done, and couldnt care less if I even have one...hell, come to think of it, most of them probably dont even know I have one...LOL...I essentially got one so my friend who owns the gym I train at can maintain the fact that all his trainers are certified...
holy