When tax time comes, it'll be a whole lot easier to get your books in order if you have a separate account for your business. It'll mean you won’t have to spend hours trying to work out which transactions were for your business. If you use a bookkeeper or accountant to do your tax, you won’t have to pay them to sort out what’s business and what’s personal.
Also, once your business starts using accounting software, having a separate business account will make bookkeeping a lot easier. That’s because many accounting packages now can integrate directly with your bank account, to automate a lot of the bookwork. For example, you could connect software like Xero, MYOB or Quicken to a NAB Everyday Business Account, which has no monthly fees.