The codes unlock things like money multipliers and other cheats.
There's quite a sizable list here. An extract:
Head to the Wiseacres Wizarding Equipment in the Leaky Cauldron hub area. It can be found in Diagon Alley. You can enter the following codes upstairs for the desired effect.
- AUC8EH - Carrot Wands
- H27KGC - Character Studs
- HA79V8 - Character Token Detector