Brenda highly encourages those families to do so. You don't know where you may go next, or what you may choose to do in future years, so it's good practice to keep your child's records.
Fun fact: The reason that portfolios are part of the home education law in the first place is because Brenda's husband, Craig Dickinson, was a defense attorney. He knew that if homeschoolers were not required to keep portfolios, most of them wouldn't. If he ever had to go to court to defend a home education family, he wanted those families to have records to prove they have been educating their children.