The Arduino Prototyping Shield makes it easy for you to design custom circuits
You can solder parts to the prototyping area to create your project, or use it with a small solderless breadboard (not included) to quickly test circuit ideas without having to solder.
It's got extra connections for all of the Arduino I/O pins, and it's got space to mount through-hole and surface mount integrated circuits.
It's a convenient way to make your custom circuit and Arduino into a single module