Control Flow:Control Flow is part of SQL Server Integration Services Package where you handle the flow of operations or Tasks.
Let's say you are reading a text file by using Data Flow task from a folder. If Data Flow Task completes successfully then you want to Run File System Task to move the file from Source Folder to Archive Folder. If Data Flow Task failed then you want to send email to your users by using Send Mail Task. The Precedence Constraints are used to control the execution flow.