To me a combination of the mentoined approaches seem to work well.
Sometimes I simply walk around and observe to identify problems and explain this for the entire group. At other times I help out couples with their specific problem and move to the next. And also I join in to feel their technique.
I guess it depends on what you are working on in class (in relation to the group) what works best. For the last few years I teach, but have no regular training with the exception when my teacher vists my country, or I visit him. But this only happens a few times each year. Yet I advance, both in understanding and ability.
Only the method of training has changed.
Like someone stated: it is easy being told what to do, much harder to find out yourself, but also more rewarding and I think better.