When to use unattend.txt

Okay, I know that you use winnt.sif when doing unattended installs w/ the CD-ROM and that sysprep.inf is used to answer the mini-setup questions in Sysprep, but when is unattend.txt used?
Is it only used when installing WinXP over the network?
Ex:
winnt32 /u: \\server\folder\unattend.txt
Is it only used when installing WinXP over the network?
Ex:
winnt32 /u: \\server\folder\unattend.txt
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