SSIS Expressions are USED for filtering information based on parameters and conditions to get desired information. They MAKE lives easy by helping to work with conditions, loops, and dynamic connections. The expression could consist of symbols, literals, identifiers, operators, and FUNCTIONS. They are mainly used for updating properties dynamically at runtime. Once we have the expressions ready, an expression evaluator parses this expression for VALIDATING the rules of the expression.
The expressions are used for the below 2 cases:

• Control Flow:
  • Here, the VARIABLE values are derived using other variables employing expressions.
  • For validating any condition, precedence constraints are used.
  • Used for setting properties dynamically at runtime by tasks and containers.
• Data Flow:
  • Expressions are used on rows to get conditional split transformations evaluating to true or false.
  • Helps to create a new column based on the result of applying expressions to get derived transformations on new columns.