Do you need a separate business bank account

A separate business bank account is a must.

1. Keep things simple, clean and efficient
It is important to keep your personal transactions separate from your business transactions.  This is particularly useful if you are registered for GST as splitting out what is business and what isn't can be time consuming and frustrating.
2. Keep Clean Records for your Accountant
Having a separate business bank account is likely to result in lower accounting fees as will mean cleaner records presented for year end compliance.
3. Prove you are carrying on a business not a hobby
The tax office is interested in whether you are running a business or a hobby.  Keeping a separate bank account is a good way to show that what you are doing is a business.