See Optimization in Typed Racket in the guide for tips to get the most out of the optimizer.
Typed Racket provides a type-driven optimizer that rewrites well-typed programs to potentially make them faster. It should in no way make your programs slower or unsafe.
Typed Racket’s optimizer is turned on by default. If you want to deactivate it (for debugging, for instance), you must add the #:no-optimize keyword when specifying the language of your program: