The cache makes much more effective use of a small SSD. A base Windows install contains a huge number of crap files that you never use, or very occasionally during say printer installation. No reason for these to be using up 80% of your SSD.
In fact, trying to install Windows 8 on a 24GB partition is a recipe for problems as Windows Updates grow the installation. If you run out of space on your boot drive, it's game over. My
C:\Windows directory (Win8 Pro 64-bit) totals over 33GB, and while the actual space on disk is less due to hardlinks, you'd hit 24GB really quickly.
If you had a 60GB SSD, installing the OS on it might be a reasonable thought. But not with 24GB. And even then, the ability of the cache to selectively store files and blocks of files that are frequently used and leave other files in the same directory on slower storage might still be a bigger advantage.