When you are debugging stored procedures, you can set line breakpoints and variable breakpoints. Both breakpoint types are saved upon termination of a debug session.
When the workbench is running a stored procedure and encounters a breakpoint, the stored procedure temporarily stops running. Execution suspends at the breakpoint before the statement is executed, at which point you can check or edit the contents of variables. You can then step over (execute) and see what the effect of the statement is.
With the debugger, setting breakpoints is easily accomplished by way of pop-up menus in the editor and Variables view. Once set, you can disable breakpoints so they do not suspend execution and then, later, enable them again.