It would be extremely useful to be able to make direct transfers between all accounts and all pots. A key example is from a personal account to a bills pot in the joint account - say your income comes into your personal account, and rather than having to make two transfers every time - one to the joint account, and then another on from there to bills - you can just send the money directly where you want it.
Compounding the extra moves that are necessary is that moving money like this also really messes up the spending summary on all the accounts involved.
Similarly, it would be great to be able to transfer from a pot within your personal account, to anywhere. The use-case is “income smoothing”, i.e. you don’t get one simple salary payment every month from an external source, but instead “pay yourself”, from a pot which itself is aggregating other income sources, which have different frequencies to your outgoings (most outgoings are monthly).