See previous discussion here: https://www.wikitree.com/g2g/1075843/upcoming-ancestry-data-purge-august-1st-please-object
And another here: https://www.wikitree.com/g2g/1075023/ancestrydna-matching-white-paper. That G2G thread includes a link to the updated Ancestry Matching White Paper that offers some explanation about the matching relevance and impact.