The "BPC_HandGrabCollisionUpdater" is a component that helps with physics/collision errors between your pawn and the object you are grabbing.
Since the Player Pawn can interact with any Object, it will cause bigger Objects like the Crowbar or Rifle to collide with your Body. This can cause issues when aiming while Shooting for example. To prevent this, use the Collision Updater Component when needed. It will automatically change the current Collision Profile of the Root Primitive Component (Static Mesh) to ignore the Player Pawn.
Primitive Components need "Simulation Generates Hit Events" enabled for this to work!
The Collision Updater can also register if the object is currently colliding another object.
This is especially useful for the Physics Pawn, where any object you are holding can cause your whole body to move around. Using this functionality, the hands of the physics Pawn can decide wether or not to use the PD (Parent Dominates) constraints or not, reducing unwanted body movement and only allowing it while the hands or object is colliding with the world.