As we've said, you misunderstood what the speaker was talking about.  So you will never find it written because you misunderstood something.

It has to do with when the 8829 is limited due to the business income limitation on Line 7 of 8829.

It USED to be said that even if it is limited (such as a loss on Schedule C), you can still take the mortgage interest and taxes on the 8829 in the current year.

But a court case (and thereafter the IRS) determined that is only allowed if you Itemize.  If you don't itemize and they are being limited on the 8829 due to business income, you can no longer take the deduction on the 8829 for the interest and taxes.  They would be carried to next year.

But if the office expenses are NOT being limited, there is no effect and it is treated the same as it always has been.