Inherited Vault Store and Indexing Service

Hello,

First of all we use EV 9.3 for Exchange Archiving.

I'm a bit lost in all those places where you can define which vault store and Indexing services you can use.
I have it defined in the VAC

1. On Exchange server with the override checked in : Targets\Exchange\Exchange Server

2. nothing in the Provisioning Group : Target\Exchange\Provisioning Group

3. On the EV Server : Enterprise Vault Servers

I am right to thing that a mailbox from Exchange Server A gets the values from point 1

If yes what is the use of setting the values in point 3. ?

Thank you very much for any clarity.

Sandrine