The present perfect continuous emphasises the action and its duration, whereas the present perfect simple emphasises the result.
Compare the following:
'I've been baking cakes all morning.' versus 'I've baked twelve cakes.'
Let's say that you started baking cakes at 9 am. It's now midday, and you've finished baking. Note that the actual time period is the same for both sentences. In both cases, you baked for three hours and you've just stopped. The difference is not in the time period or whether or not you've finished - the difference is in the emphasis and focus of your sentence.
So if someone says, 'How many cakes have you made this morning?', you'd answer, 'I've made 12 cakes.' The focus is on the result. But if someone says 'Why are you tired?' or 'Why haven't you done your homework?' you would explain by saying 'I've been baking all morning'. Here the focus is on the activity.
I hope that all makes sense.