Clarification on "shared /var folder" used for Exchange backups?

Can someone provide me some perspective as to whether there is any "non-Avamar" need for the "shared /var folder" used for Exchange backups when the customer has a newer Exchange environment (which apparently seems to have no real need for a "cluster shared folder")?

Every so often I encounter a customer running a newer version of Exchange, and they are almost "militant" in their questioning of why they need a shared folder that apparently will exclusively be used for the Avamar DAG backup configuration - presumably because Exchange no longer needs such a folder. That is what I am trying to get clarification about.

Also, I do understand that one could use the "proxy based" approach for the Exchange backups, which appears to eliminate the need for both the DAG client and the shared /var folder. Can anyone speak about "compelling reasons" NOT to use the proxy approach, including clarification of why there might be "local databases that are not part of the DAG" (something that to me seems counterproductive to the whole DAG concept).

Understood that this has more Exchange aspects to it than Avamar, but it does relate directly to the configuration of Avamar for Exchange DAG backups.

All comments/feedback appreciated - thanks.