When you watch TED to learn English, in addition to training your listening skills, you can also improve your reading and writing skills through looking up single words, using documentary idioms, etc.
When learning English while watching TED, in addition to training listening skills, reading and writing skills can also be improved through word searches, documentary language usage, etc.
When watching TED to learn English, we can not only train our listening ability, but also improve our reading and writing ability by looking up vocabulary and documentary usage.