Zero-Percent Certificate of Indebtedness

I bought another $1000 I-Bond at Treasury Direct today, after reading various things about where the interest rates might be headed on these. (see here and here, for example)
The weird thing I noticed on Treasury Direct is this thing called a Zero-Percent Certificate of Indebtedness. You basically would buy this so you can have money ready in your account to buy other bonds at a later point. I have to say, I don't see the point. That would be like if your bank said you could open a no-interest account and put money in it so you could then conveniently transfer it to your savings account whenever you wanted to start earning interest. Why would anyone need that in-between step?
Given that you can automatically transfer money from your bank account into Treasury Direct anyway, and given that the minimum purchase is $25 for an I-Bond, this C-of-I seems like a pretty stupid thing to offer.
The other nice thing is that I noticed that my existing $2000 worth of I-Bonds is now actually worth $2116.40. (A tip o' the keyboard to Caitlin at Clutter to Cash for inspiring me to actually update my bond values in Quicken!)