Reprocessing is a new feature in Sentry that allows iOS developers to reprocess events from error monitoring that cannot be processed due to missing debug symbols, holding them in the event stream until the symbols are uploaded, reducing noise and preventing email notifications from being sent out prematurely. The feature can be enabled or disabled in project settings, providing an additional layer of control for developers. With reprocessing, events that lack mandatory debug symbols are put on hold and will not show up until their symbols are uploaded, ensuring accurate symbolication and reducing bad grouping. Developers can also trigger reprocessing manually through the API or command line tools.