Kendra Document Storage purpose

According to Kendra pricing information, https://aws.amazon.com/kendra/pricing/ Kendra Developer Edition (KDE) has a limit of 10,000 documents that can be stored in Kendra Document Storage. I believe, Kendra can scan up to 500,000 documents using KDE (monthly limit).

Let's say source folder has 100,000 documents and I use KDE with 10,000 documents limit for Kendra Storage. I am going to search my document source using Kendra Search. Will 90,000 documents which are not stored in Kendra Storage be still searchable? If the 90,000 documents are still searchable, then what is the purpose of Kendra Document Storage? I intend to do Kendra scan once per day.