CATS (Cross Application Time Sheet) is a tool in SAP for recording employee time across different business areas like HR, Project Systems, and Controlling. It allows for a single entry of time data that can then be distributed to various SAP modules. CATS provides benefits like integrated time collection, approval workflows, default values, and interfaces for various user types. Time entered in CATS can be transferred to HR for payroll, Project Systems for project costing, and Controlling for internal order costing. The integration enables accurate time tracking and cost allocation across key SAP applications.