Von Ulmer's safe key *potential spoiler*

The key has a label with “SVU - safe in study” on it…

the description says. Without spoiling something, please, does this mission item have a purpose later in the game? Because all the safes I have found in his villa are open.

EDIT: You get the safe key during the “Empty Spaces” mission. Here it is, it is the last of the mission items:

Yes, it does. The thing you need it for unlocks after you do a bunch of other stuff.

Huh. Ok, now I have played through it all. Did not notice I needed it. What was it for exactly?