By activating this you make the deliberate decision to permanently sacrifice a portion of a chosen power in exchange for a temporary, immense boost to it. Months of growth are scoured away in minutes in exchange for allowing you to challenge beings vastly greater than yourself. Weakening a simple mage hand might allow you to throw buildings around, while sacrificing a Keystone could break the universe itself.
While you can precisely control what parts of the affected power are sacrificed, anything that is not lost will also not be boosted. Any effect that would serve to restore your powers is slowed down, so recovery takes no less time that it took for the sacrificed capabilities to be developed.