Is it safe to reinstall Windows without first decrypting the whole drive?

I am using TrueCrypt’s ‘Full Disk Encryption’ and according to TrueCrypt’s FAQ I should ‘Permanently Decrypt System Partition/Drive’ before reinstalling Windows. This does not make any sense to me. Would reinstalling Windows not undo the encryption in the first place?

The reason I would like to know, is because ‘Permanently Decrypt System Partition/Drive’ will take a long time.

Note: If the system partition/drive is encrypted and you want to
reinstall or upgrade Windows, you need to decrypt it first (select
System > Permanently Decrypt System Partition/Drive). However, a
running operating system can be updated (security patches, service
packs, etc.) without any problems even when the system partition/drive
is encrypted.

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