From Xojo Documentation
Allows you to create cells which vary in height based on their content. The default value for this property is False to maintain backward compatibility.
Set this property to True to have the table's row height vary based on the custom cell inserted into it. This is useful if you have different sized custom cells you want to place in the table.
You can also dynamically change the custom cell's content to have the table row height change, but you'll want to change the autolayout constraint for the custom cell when it is added to the table.