Knowing the default password would be very useful when your computer prompts you for one you don't know, like the password for the Administrator account.
There are a number of situations where having an XP default password would come in handy. For example, if you don't know the Administrator password but you're diagnosing a serious problem and are accessing the Windows XP Recovery Console, the default Administrator password would sure be nice.
Or maybe you're trying to boot into Windows XP Safe Mode. The default Administrator password could certainly save the day here.
While there may not be an actual default XP password, there are other ways to accomplish the things you wanted to get done with a default password:
"Windows won't start at all so I need to get into Recovery Console to fix the problem but I don't know the Administrator password. I really needed a default XP password so I can get on with fixing this problem!"
Every Windows XP computer has an Administrator account and there are ways of finding the password configured for it: How To Find the Administrator Password in Windows XP. No default password required.
You should also know that some other diagnostic areas of Windows XP that seem to require access with the Administrator account actually don't. Your user account can also have administrator privileges which is enough to satisfy the requirement. Safe Mode is a perfect example of this in Windows XP.
"I really needed a default Windows XP password so I could get into my account. I completely forgot what I set my password to!"
You don't need a default Windows XP password if you've forgotten yours. There are actually several different things you can do if you forgot your XP password and need back in.
See I Forgot My Windows XP Password! for several ideas including how to successfully guess your password, using a Windows XP password reset disk, and using special software to recover or reset the password.
Looking For Default Password Information for Another Version of Windows?
The solutions to the default password questions above are specific to the Windows XP operating system so if you're using another, see What Is the Default Windows Password? for a discussion based on your version of Windows.