Answer:
The main disadvantage of LBP (lead-based paint) is the health hazards associated with exposure. Thus, in the U.S. LBP was banned from residential housing and child-occupied facilities in 1978. LBP, especially in high friction areas (door jams, window sills, etc.), is broken down into dust which tends to settle in areas easily accessible to small children who can inhale it or ingest it through hand to mouth action.
Long and short term exposures to LBP may lead to a number of documented ailments, however exposure in children can have the most profound effects. Lead has been shown to effect neural development (among many other things) and at even relatively low levels of exposure will retard normal brain growth and permanently decrease IQ.