The COALESCE function in Snowflake returns the first non-NULL value from a list of expressions, helping to manage NULL values and prevent disruptions in calculations. It's like finding the first available seat on a bus, moving through a list of expressions until it finds a non-NULL value. The basic syntax for COALESCE involves checking each expression in order, stopping when it finds a non-NULL value, and returning that value if everything is NULL. Common use cases for COALESCE include replacing NULLs in queries, handling NULL values in calculations, concatenating strings without NULL issues, and providing default dates. However, it's essential to be aware of the differences between COALESCE and other NULL-handling functions like IFNULL, NVL, and NULLIF, as well as some best practices when using COALESCE, such as data type inference, date handling, and performance considerations. By understanding how to use COALESCE effectively, developers can write robust and maintainable SQL queries that handle the unexpected with ease.