Quite correct,
What it actually does is to duct cooling air around the turbine casing, thus reducing engine turbine tip clearances to a minimum and therefore blade tip losses (it works in conjunction with the active turbine clearance control system).
However because tip clearance is at a minimum there is the possibility of blade tip abrasion and higher EGT. Each BUMP is recorded in the tech log because after a certain number the function is no longer allowed to used unless the engine is overhauled.