Thomas,
I have observed that some students have only really vague ideas about the profession they're about to enter. Activities like the field trip and/or guest speaker can open eyes and give a vision of a future that could truely change lives (of the student, their family, workplace encounters, experiences, etc.). Can be quite motivational to the degree that marginal students buckle down, and average students ramp it up a notch or two.
Barry Westling