Clarification: I'm talking about the INNER airlock door.

Keeping the airlock closed in-between spacewalks sounds safer:

• In case of accidental puncture of the outside of the module, this has no effect on the rest of the station.

However

• This removes a (little bit) of livable space for the astronauts
• It will need to be actually opened up again once you'll want to depart.

So what do they actually do ?