This was a revolution in poetry as poetry in earlier times had a pedantic function. A similar revolution occurred in Romantic medicine. Doctors were expected to listen to their patients' complaints, taking a history much like the wanderer of this poem takes the history of the leech gatherer to gain his enlightenment. Like the wandering poet, the physician is a being with a higher level of language and knowledge. The leech gatherer also reveals the economics that underlie medicinal practices.
Someone has to gather the leeches.
Notice that Wordsworth finds the gatherer's oppression ennobling. Suffering and joy go hand in hand. Source Poetical Works Editors Thomas Hutchinson Publisher Oxford Univ. The Poems Editors John Hayden Publisher Yale Univ.