Right now if you want to run a report across all client accounts in your agency account, you need to manually create a new account grouping and then add that grouping to each of your client accounts.
If you think about that when you first set up all your accounts, it's not a problem. However, if after you've already made all the accounts you realise that's a thing you'd like to do, it's quite a pain to go back through and do it.
I propose that it would be useful if all agency accounts came with as default an Account Grouping that consisted of all client accounts and stayed updated automatically as you added new accounts in. This would be a useful functionality that would probably save all of Ninjacat's users a decent amount of time as running a top-level report on everything is a pretty common desire (I imagine).