What's the different between Instances and Instances(Particapation) in Data Warehouse

The Instance returns the number of hits when the variable was set with a value (the beacon included eVar1=value).

The Participation metric presumably returns the number of hits when the variable was either set or the previously set value was persisted according to the eVar settings.

I doubt the participation here refers to the attribution model as the participation should be configured with the date range the hits are processed within (e.g. Visit, Visitor), but the DW does not point to this at all.

It seems the current documentation does not have any reference to the participation type of metrics available in the DW template builder.