Paolo and SDF_Traveler, among others, are correct. You don't retract flaps during the landing cycle, they are almost always retracted after exiting the active runway. Although there are many good reasons for retracting them, a common one is ground personnel and equipment. In the landing configuration, most commercial airliners' flaps extend significantly downwards, not only causing potential to interfere with ground equipment (fueling, baggage, maintenance) but also causing potential to damage the flaps themselves. Since the flaps are often one of the more intricate parts of the airframe, using sliding tracks, jackscrews, etc., repair is often costly and time-consuming. Fully extended flaps at the gate can also cause injury to personnel working around the plane and not noticing them; for this reason some airlines paint the extemities of the flaps with hi-viz colours (KLM's MD-11s come to mind). Finally, especially on large aircraft (e.g., 747), it's a good idea to retract the flaps before taxiing back to the gate; when fully extended, there is actually relatively little ground clearance on a large aircraft's flaps. And if you notice the taxiway configs at many airports, you'll see that often the taxiways are narrow enough that the outboard engines on a 747 will actually be outside the confines of the taxiway edge lines (yellow lines). So, having the flaps down when the plane turns a sharp corner further decreases the safety margins when clearing obstacles that might have been left too close to the taxiway (vehicles, equipment, even taxiway signage).