I have to repair 100% intact tank

Tanitha: Modules etc that are damaged, don't effect your tanks hit points. So you can still be on full health but have damaged modules that need repairing after battle. The "Remove speed governor" clearly states it damages your engine, Damage that obviously needs repairing after the battle.
Unlike other equipment that is a one use 3k each like the repair kit, With the speed governor its reusable and you pay for the repairs to the engine after the battle, you can use them or not, its up to you.