dbt macros are reusable blocks of SQL or Jinja logic that help simplify and standardize data transformations across multiple models. They enable you to create flexible, dynamic SQL by leveraging Jinja features like loops, conditions, and variables. Macros can be used to standardize column names, convert data types, handle NULL values, ensure cross-database compatibility, test and validate data, and maintain project consistency. By using macros, your team can ensure that everyone follows the same process, reducing errors and discrepancies in the data pipeline, while speeding up development with reusable logic. Macros are essential for large-scale projects as they promote consistency, reduce redundancy, and accelerate development by making it easier to manage complex SQL transformations.