Pitched ceiling and wall cavity

Hi all,
So, I have a second storey bedroom in my new place and the house has pitched ceilings.
Had a trade point out to me that the rooms are wider on the ground floor and that the bedrooms upstairs have a cavity behind the wall on both sides.
One side has some air con ducting but I carefully cut a hole to look in the other side and I think I may be able to use this space to build in some bedside cabinetry or wardrobes etc.

Is there any reason for this cavity? Only reason I can think of is to make sure the wall isn't stupidly low. I've found the plans and it is marked as "open space".

any issues with using this space?





(I might need to make one thread for my reno instead of one for each little question.. lol)

we call this a "ghost hole". Its where ghosts live. You should sell and move.

haha pls don't mess with me like that... if my wife hears that then, yes, we will be selling and moving

no need for me to mess with you. you'll be messed with soon enough.

Ha Ha.... Too small to hide contraband
Tho, could be a selling feature?

whatever you use the space for, it will be outside the insulation envelope
so allow for new insulation