This option stops the session if it encounter errors in the transformations by default its value is 0 but the best practice is set the value to 1.
Consider the following scenario:
In source there exist a column named 'Amount' with datatype number in a table whereas in target the corresponding column has datatype as number(22,5).
By having default value '0' for Stop on errors , this session never fail even there exist some data truncation
When we get the stop on errors to '1', the session will get fail when it encounters a data truncation problem.