I like using ctrl space to close the content window , but it should be a toggle.
CTRL+SPACE open content window
CTRL+SPACE close content window
At the moment it is an annoyance.
Think about adding an asset.
CTRL+SPACE to drag and drop the asset, do the import, content window closes
CTRL+SPACE to then edit the asset, setting materials , scaling, et al, content window closes
CTRL+SPACE to then get to the game object and add the asset to it. Content window closes
CTRL+SPACE to then get the game object and add it to the scene. Content window closes
You are constantly hitting CTRL+SPACE
Would be a really, really nice feature if you just made that one small change
Perhaps you could add a vote to this thread to see if other people agree with me?