I already had a home-built 5V power supply and wanted to make it easier to connect up to range of Arduino microcontrollers and various add-on modules. By including this little DC-DC converter within the box, I was able to branch off a 3.3V supply from the existing 5V. A tantalum capacitor was added on both input and output to minimise the risk of high frequency noise leaking between the two supplies. I used araldite to stick 3 rows of jumper pins onto the top of the box - for ground, 3.3V and 5V. It works perfectly and fixed some problems I was getting with the NRF24L01 module.