Using the inj. pump locking pin

[300 Super D]

Can someone explain how this is used? I assume you put it in when installing a serviced pump to keep it from moving? What about when removing it?

I was wondering if you could put it in before removal (not sure how though) so you can put the pump exactly back in place by locking it again before installing, to keep the timing perfect? I guess Im paranoid about not being able to set timing as perfect as it was.