For generations, Los Angeles County-USC has been seen as the hospital of last resort. But as the crowded hospital moves into its new, smaller home, officials have a message to its most frequent users: Please, please stop coming in so much. Because the hospital serves the poor and uninsured, some patients come back time and again, contributing to overcrowding. So about four years ago a Los Angeles-based nonprofit was asked to study why some patients visit the emergency room so frequently.