For me, it's about the ability to send/receive funds overseas as a local transfer and hold in that currency at a reasonable exchange rate.
For example, if my cousin in the UK wants to send me money for something, she can send it to my TransferWise account using a UK sort code and account number rather than having to pay for an international transfer and losing money in the exchange to AUD. I can then hold the GBP to use at a later date or convert into a different currency, e.g. EUR or USD. Now with the debit card, I can access the funds through ATM/EFTPOS rather than via online transfers.
I also have Citibank multicurrency accounts attached to my Plus transaction account, for travel, so I am keen to see how they compare.