Some other benefits to using TrueCrypt full disk encryption:
1) It is much faster than a disk wiper. When you are ready to wipe the disk, just change the password to something long, random, and not committed to memory. It literally takes minutes versus the hours or even days if doing the traditional wiping method like with Active Killdisk, etc
2) In some limited use cases it adds an extra layer of security even if you use weak passwords and even if your attacker knows your password. For example, assuming he/she was a house guest/ roommate and not law enforcement and didn't have a write-blocker to clone your drive, assuming you agreed to share your computer with him/her but kept separate Windows profiles.... lets say he she was nosy and while you were away on vacation or out shopping or taking a shower he/she wanted to get into your Windows user profile by cracking your Windows password (very easily done with a bootable live cd) or read your private files by using a livecd and mounting the NTFS, well this will not be possible to do if you have TrueCrypt full disk encryption! In fact, not only can you use a weak password, not only can you share your TrueCrypt FDE password, (something you kinda have to do if you are sharing computers with someone), and not only does the harddrive not even need to be 100% encrypted, but as long as FDE is in place, no one can use a livecd to mount to NTFS or boot to a CD to crack your Windows passwords! At least not until they 100% decrypt the drive and uninstall TrueCrypt FDE, but likely by that time they will get caught and noticed since it would take twice the time to re-install FDE and put it back and re-encrypt the drive! Plus if you had burned the rescue disk from iso, you would have realized something was wrong the next time you boot up from the disc!