Failure of SC 1.3.1 due to summary attribute in layout tables

On F46, Failure of SC 1.3.1 due to using th elements, caption
elements, or non-empty summary attributes in layout tables, is
explained that using summary attribute for an layout table is an
error. I dont understand why, or maybe explanation is a bit confusing.

"Do not include a summary attribute and do not use the summary
attribute to describe the table as, for instance, "layout table".

Do not include at all or not use summary for a description not
explanatory on table scope?

Example code also is terrible ...

thanks
Livio

<http://www.w3.org/TR/WCAG20-GENERAL/#F46>