What are the default setting for Event Expiration in AEP?

Hey @vin_adobe 

There is no default event expiration set from Adobe's end. If you want to enable expiration as mentioned in the link that you shared, you need to contact Adobe support and the engineering team would enable expiration.

As for the best practice, that varies from business to business. What might work for one business might not work for another. Here's a very awesome post about it from Danny Miller detailing out the different approaches. https://experienceleaguecommunities.adobe.com/t5/adobe-experience-platform-blogs/multi-forked-event-expiration-strategy-using-datastream-in-aep/ba-p/593224

Hope this helps.

Cheers,

Abhinav