Intended for race only use or for special applications, like the Yamaha V Max complete induction kit. Stage 7 kits are designed to optimize jetting for a given tuning specification or racing conditions.
This wont necessarily give you a power increase. The jet kits are designed to help jet the bike accordingly when installing aftermarket performance parts such as exhausts and air filters. They can also help with jetting the bike for elevation even if the bike is stock. If the bike is not jetted correctly currently, then you will notice a power increase as the bike will run properly after this is installed.