The use of explicit conversions, or casting, is helpful when compiling in strict mode because there may be times when you do not want a type mismatch to generate a compile time error. This may be the case when you know that coercion will convert your values correctly at runtime. For example, when working with data received from a form, you may want to rely on coercion to convert certain string values to numeric values. The following code generates a compile time error even though the code would run correctly in standard mode.
var quantityField:String = "3";
var quantity:int = quantityField; // compile time error in strict mode
If you want to continue using strict mode, but would like the string converted to an integer, you can use explicit conversion:
var quantityField:String = "3";
var quantity:int = int(quantityField); // explicit conversion succeeds
In strict mode, the compiler tests for type compatibility with the is operator. If the is operator would return false, the compiler generates an error.