I'd been working for a good number of years as a mechanic (including suspension servicing, disc brake servicing, full-suspension frame servicing, wheel building, etc.) before ever going nearing Cytech training
it was moving from my last LBS to a big chain-store retailer (Evans) that actually got me onto Cytech training, which was paid for by the company.
Cytech II was fantastic as we had one of the best trainers in the industry working in-house for Evans at their LCW site in Bermondsey
I learned a huge amount of extra detail and information, including much of the theory side I'd never thought much about.
Came away with some solid literature ( a huge binder ) which I have regularly used in the time since for reference and as legal defence (BS6102) for not undertaking dangerous work despite a store manager insisting a job "should be done".
Working under severe time pressure during the Cytech final exams was also interesting and very revealing, similar to that feeling of panic at the start of a run in a DH race!
Is Cytech essential? No, experience counts for a huge amount.
I have interviewed mechanics with Cytech II I would not employ in my workshops, because they were not competent. I have also interviewed "time served" mechanics with no formal training that I would also not employ because of bad practises and attitude problems.
I'd say a combination of formal training, on job experience and certification is ideal.
From an employers point of view, a Cytech or C&G qualification is something you always look for on a CV, and can be the difference between getting a job interview or not, when we have 10 CVs to go through.
MOST IMPORTANTLY for any mechanic..a willingness to constantly learn, admit when you don't know something (and ask for help), and be prepared to change your ways of working if new, better ways become evident.
I really enjoy a day when I learn something new (I learnt something crucial about Shimano Di2 setup yesterday, that Shimano's own training did not cover). I will always admit I don't know everything, no one can.
Any mechanic who says they know everything is dangerous in my opinion, and often resistance to change.
The more knowledge you can gain, the better you can be.