In some ways a visa application should be thought of in similar terms to a job application. Admittedly in the case of visas, there generally needs to be a reason for your application to be rejected, rather than a reason for it to be accepted, but at the end of the day, you want to visit a country and you need approval for that visit to take place. It therefore makes sense to make your visa application as attractive as it can be.
Of course, visa applications are a more like standardized job application forms than a CV in that there are a number of standard fields, which need to be completed and completing them fully, correctly and accurately is crucial to having your application accepted. In some cases it may help to look for a translator with specific, localized knowledge, for example a translator in Melbourne may be able to double-check any local references on your application more effectively than a NAATI accredited translator in Darwin at the opposite end of the country. In many cases, however, where in the country the translator is located is irrelevant.
The key point is to ensure that your document contains all the information an official needs to feel comfortable approving your application. Ideally the form should project a respectable and professional image, which is part of the reason why having it translated by an experienced NAATI translator can be crucial to success. In short, presenting an application in perfect English, which is completely free of any errors of spelling, grammar and punctuation is a clear signal that you are serious about your visa application and understand your obligation to act in a responsible manner when visiting Australia. This can vastly improve the impression it gives and thereby increase the chances of it being approved.