Positives = the potential of saving many lives obviously. As theres a severe shortage of organs being donated, not enough lives are being saved as there could be. People are dying through suffering and we have the chance to save them and give them a second chance at life.
negatives = Scandals whereby doctors have been accused of 'inventing death' in order to retrieve organs. Definition of death isn't completely known and varies from country to country. For this reason, many people who would otherwise not be pronounced dead are being pronounced dead so that the organs can be obtained in a fairly fresh condition. Usually complete cessation of the brain stem (medulla) would mean that someones dead, however with a potential donor they are pronounced dead before total cessation so that the organs can be of some use.
Hope I helped!