Allow to change subnets modification with enabled vnet peering
Currentl once vnet is deployed and peering is created with another subscription or vnet. Once the peering is set, it is not possible to extend,remove or add another subnets ranges to all vnets which have valid peering configured. For such if you need to modify the subnet, you have to remove the peering (might cause downtime if peering is used), do the subnet modification and recreate the peering again.
For an enterprise that uses a hub and spoke topology this is a must. Otherwise, we are breaking all traffic going though NVA (Firewalls) each time there is a change to an address prefix or subnet.
Bart Danse commented
Not only subnets also additional adress spaces have the same limitations.
Reda Mousbir commented
Indeed this is a cumbersome process when you haver 50 peerings but you should also make sure you have all your ranges defined up front. It just prevents from having an easy way to reclaim or update IP space.