, you can back up multiple shares with a single plan, but you gonna need a license that supports a sufficient number of shares. Please check the license comparison page.
Thanks

Considering that all my data can be backed up with either multiple plans for each share or a more expensive single plan covering multiple shares, is there any real functional advantage to the latter beyond convenience in seeing up mite plans and schedules?

seeing up mite plans = setting up more plans

The main advantage would be indeed a convenience granted by controlling the entire backup with a single plan (scheduling, retention, etc.) as well as the fact that you wouldn't need to worry about eight plans potentially conflicting / slowing down the performance of each other as they use the same destination.

What's disgusting is that this is a loss of functionality.

I have just fired off a very irate message to CloudBerry as I've had to migrate a client to a new FreeNAS server due to a disaster and just found out we can no longer do this.

The same subscriptions we've always had let us this but now existing plans using multiple mapped drives/UNC paths can no longer be amended or even new plans created to backup those shares on a single server.

We have to use this functionality to backup this FreeNAS server via a Windows machine, now that we've had to migrate that to another box I can't do it.

Asked for a refund as the licenses were recently renewed and I won't be buying more when anymore expire, it's contemptible.