This is where you'll find Clara most of the time, for one thing. She has a briefcase that you can highlight, but you can ignore it till someone tells you to open it near the end of the game.
There are also three portraits and two books in here that you might find useful.
What am I supposed to do with all these paintings?
Also, next to the door is a table with a lovely silver tea service, in case you're thirsty --
-- or in case you ever have any need for oranges or napkins, for that matter.
How do I recharge Jessalyn's phone?
Finally, there's a loose board in the floor in front of the tea service. You can't click it at first, but come back here after you charge Jess's phone and listen to her journal.
How do I solve the puzzle under the floorboards?