Trying to work defense, without understanding how, can create lifelong problems for a dog. For example, if a helper mistakenly overloads a dog's defensive drive, it can create avoidance and insecurity in the dog which, in turn causes the dog to not respond confidently to the helper and may ruin the dog for the work. This is why I believe helpers should have some kind of apprenticeships in order to be competent enough to work dogs in protection, for their sake, and the sake of dogs they are working. It is unwise for a novice helper to work young or inexperienced dogs when he starts out, as any error in a young dog's early traiing can have a bad impression, and a bad impressin is a lastig impression. This also may cause friction between the helper and the handler, and obviously this is not desirable.
Helpers get the glory and the blame.
The helper must work hard, usually for no money and oftentimes little appreciation. In our Schutzhund club, the helpers do not pay dues, nor do they pay for seminars or meals at club functions. The club also pays for the helper's scratch pants and cleats and basically tries to keep their helpers happy. A top helper can make a Schutzhund club successful. Being a helper myself, I am pro-helper, but I'm sure you can see my point.