If you have enabled Time Machine, the disk space could be taken up by local snapshots. When local snapshots are enabled, Time Machine saves snapshots to /.MobileBackups/ when there is more than 10% free disk space. See http://support.apple.com/kb/HT4878. Local snapshots are not counted as used disk space in Finder, but they are shown under backups in the About This Mac window. The snapshots are deleted automatically if disk space is low enough, but since 10.9 the newest snapshot is kept even if there is less than 10% free disk space.
To see what files take up disk space, you can use OmniDiskSweeper:
To include folders like /.MobileBackups/, open OmniDiskSweeper as root by running sudo /Applications/OmniDiskSweeper.app/Contents/MacOS/OmniDiskSweeper.
You can also just use Finder. Run sudo defaults write com.apple.finder AppleShowAllFiles -bool true;sudo /System/Library/CoreServices/Finder.app/Contents/MacOS/Finder, open the root folder in list view, and enable calculating all sizes:
So, it this is not a direct answer to your question because it is kind of a work around.
I totally agree with not having / wanting to spend more than you initially should have, but I think we need to start changing our mindset a bit. PC's and MAC's alike are coming with less internal storage options and somewhat force you to rely on the cloud and / or external storage.
So with that out of the way, this my workflow - I have a 128GB MBA, so I am in a similar position as you.
I bought am external USB3.0 drive that I carry with me all the time.
On that drive I have my photo library and all the big stuff. I figure if I am doing anything that requires a substantial amount of work in my photos or iTunes, I will be sitting down and plugging in a drive is no biggy.
On my internal drive - I simply just have the apps and I only have the apps I use 70%+ of the day on my MBA drive - the rest lives on my external drive.
I also use Xcode and the latest beta takes up 7.5GB+ so that is a good chunk gone already, versus the Xcode 6 version which is 5.5GB so those 2 already take up over 10% of the drive.
So what I do is every 6 months I re-install my mac. Once when the new OS is out and once in the middle of the summer. All my data lives in the cloud like dropbox and I do not use my documents or pictures folder - they are pointing to my folders inside my dropbox folder - so all my data is save.
This way every 6 months, my temporary data is removed and I know it is, because my internal SSD is cleaned off. This process takes about a day, but it is saving me a lot of frustration.
I can appreciate not everyone can adjust their workflow around this, so to let you know I am an iOS developer and a teacher at a tertiary polytechnic so my data is super important.
Notes I store in Evernote and my files in Dropbox, iCloud I use as well, but not very much.
I hope this gives you an idea of how to help you manage this issue. It is a real pain to start of with, but if you treat your MBA purely as a data independent shell, than it may help your thinking about it a bit.
Hope it works for you :-)
Best Answer
OK so.... after posting this, on a whim I decided restarting my laptop to see if that purged anything extra, even though it was still showing the 1.76G being used. I didn't think it would make any difference, but I suddenly remembered that was always worth a try when dealing with things like this.
Gonna answer my own question by saying, once you've actually followed the above linked-thread, restart your computer!
Storage Management now shows Zero KB of space being used for "Music Creation". GarageBand is no longer the space hog it was. Huzzah!