Avid MC Training
We are Europes largest media training provider and also the worlds largest freelance post production talent agency, as such we are very well placed to assess the benefits of formal training verses self taught. Thats our background.
All the comments made so far have merit however only you can decide what method is best for you when trying to learn a new NLE. We have trained 1000's of people over the years on FCP, Avid, Premiere, Smoke and many more and one reoccurring thyme is those that are self taught do not usually have the full understanding of the software. Often self taught people learn what they need and once they feel confident with that they rarely explore deeper. There is always more than one way to achieve a result and a truly skilled editor can apply the best approach at the start of a project, if you only have one way of doing things that can limit your speed and the quality of the finished project, and ultimately the clients satisfaction, time is money does really apply here. If you are already fully conversant with one editing solution a training course will quickly give you the knowledge to transfer those skills to a new tool set, often its more about the tool set and the different work flows that each NLE offers. If you are totally new to editing a course will give you the knowledge and confidence to explore further knowing you are doing it right.
A classroom experience will short cut the learning experience and get you on the right track, but there is no substitute for experience and this is up to the individual to apply the training as soon as possible to hone the skills and get faster.
There are numerous ways to learn, online tutorials, DVDs, online training forums, learn from your peers and classroom training, each has its place and everyone is different so theres no right or wrong way, possibly a combination of methods can work, you also should never be satisfied with what you know and theres always something else you can learn, if of course you want to be the best at what you do.
The cost of a training course can be quite high but when you factor in the extra work you could apply for its only a few days work and its paid for its self.
As for certification, gaining a certificate doesnt make you a great editor, what it does is give you and future employers a yard stick on your competence and knowledge of a particular subject, only experience will make you a better editor. You can often take a certified exam without taking a course, so if you are self taught its a good way to confirm what you do know.