[Windows 8 General] GoodDayToDie:
So, five partitions. The first one is the boot partition (it's usually only 200MB and can happily fit in less, but that doesn't matter much). Don't mess with it. Technically it's only required that you use a separate boot partition when using BitLocker, but it's a pretty good setup.

The second is nearly a gig of some kind of recovery data. It's too small to be the Win8 recovery installer, so I'm guessing it's some pile of Asus-specific crap that probably isn't even useful enough to be something like a bunch of drivers that you could download newer versions of from their website; more likely its useless garbage like that wallpaper it comes with and other pointless stuff. Check before deleting it, I guess, but it should be safe to kill.

The third is your OS volume. It is, as you noted, less than 80% of the SSD's size.

The fourth is probably the standard Win8 recovery image. It's basically a Win8 install DVD, and its purpose is to allow the use of the "Reset" functionality to wipe the OS clean - essentially just automating the "format and reinstall" process. It also can be used to repair a system that becomes damaged or to manually reinstall Windows if you manage to nuke the OS partition so hard you can't use the Reset feature. This partition can usually be safely removed after writing it to a DVD or Flashdrive; there are steps and utilities for doing so.

The fifth is the real hog that's using up your space, being almost four times as large as all the other non-OS volumes put together and taking up about 18% of the total capacity of the drive. My guess is that this is the image used to restore the OS to exactly the state it was in when you bought it (Asus pre-installed-crapware and all). It's almost certainly a complete waste of space, unless you paid for a copy of Office or something when you bought the computer and the re-installer is on there. Anyhow, that partition as a whole is too big to copy off to anything except a large flashdrive/SD card/etc., an external HD, or a blu-ray disk, but it *might* be possible to mount it and find any parts that are actually of any real value and blow the rest.

If you're interested, here's what I would do (it's what I do, and recommend doing, with *any* new PC): now that you've verified that the OS boots up, the hardware works, etc, prepare a bootable flashdrive, put the Windows installer on it (should be possible to get it from the 4GB recovery volume; as I said, there are steps and utilities to do this), download all the drivers for the hardware from the OEM's site (Asus.com in this case) and put them on the flashdrive too, then reboot from the flashdrive. Choose to do a custom install of Windows, delete every single partition from the existing scheme, select the resulting unpartitioned space, and tell Windows to install there (it will set up a sane partition scheme for you). This process removes unwanted partitions, removes OEM garbage (which can be a pain to remove otherwise), gives you a clean Windows install without the horriffic tampering the OEMs like to do (interesting fact: I ran Vista, and found it just fine and far better than XP, with no crashes since RTM on my clean-installed copy... until I tried using an OEM copy on somebody else's machine - more powerful than mine, mind you - and discovered what all the complaints about slowness and crashing came from; the difference between an OEM and a clean retail copy of the OS were astonishing and painful), and puts you in control of the disk usage.