Explanation
Querying contacts from the Einstein Engagement Frequency data extension when creating the send can be used to limit the number of emails a subscriber receives to a maximum of one email every 14 days. The Einstein Engagement Frequency data extension contains information about how often each subscriber engages with emails and what is their optimal send frequency. By filtering the data extension based on the optimal send frequency, the send can exclude subscribers who have already received an email within the last 14 days.
References:https://help.salesforce.com/s/articleView?id=sf.mc_as_data_view_einstein_engagement_frequency.h