Append v/s Append To in Dynamics CRM/Dynamics 365 CE/Dataverse

Let me repost this nice and exhaustive article wrote by Sanjaya Pradhan to explain the difference between Append and Append To privileges in Dynamics CRM/Dynamics 365 CE/Dataverse security roles.

Quick summary

Append on table X means you can set the lookup columns of table X.

Append To on table Y means you can set the lookup columns of other tables pointing to table Y.

This means that, if table X has a lookup towards table Y, to make it work properly user must have Append privilege on table X, and Append To privilege on table Y.