Gateways in Multicast group

[datnus]

Hi all,
I’m testing Multicast in Chirpstack.
I can make Multicast downlink works with only adding devices to Multicast group.

Then why there is a table for gateway?
Under which usecases do we need to add gateways into a multicast group?

Thanks a lot for your help.

[brocaar]

In the current default, ChirpStack will try to determine the minimum amount of gateways needed to send the multicast downlink. However, this can be unpredictable as this depends on the received uplinks from the devices. In some cases you already know which gateways you want to use for multicast downlinks, in such case you can set this table yourself and ChirpStack will only use these gateways.

[datnus]

Thanks a lot.
I understand now.