Windows Vista Service Pack 2 (download), which was released last month, came with numerous fixes and tweaks to improve performance, bolster security, and squash bugs. But some users reported “large increases in free hard disk space after installing Vista SP2.” One user claimed that installing Vista SP2 freed up a massive 40 GB chunk of disk space. Another said, "Wow! I didn't notice that til now. I went from about 88GB free to 122GB free. That's a significant change 'under the hood,' isn't it?" And yet another reader gained back 130 GB of hard disk space.
Source:→ The Industry Standard