Jared Westover talks performance:
Often, developers use local variables when writing ad hoc queries or stored procedures for many reasons. You might hear “never repeat code” or “avoid using magic numbers.” While writing a lengthy stored procedure, I might include a few. However, did you know that local variables can hurt the performance of your queries? How can you keep local variables from negatively affecting performance? Keep reading to find those answers and more.
This is the kind of performance issue that you can easily forget about. Jared includes two methods for resolving the issue if you run into performance problems on a specific query or stored procedure.