There are situations where you may be below the $60,000 threshold for GST registration and you may choose to register. An example would be where you are making a loss, and being GST registered would mean that you would receive GST refunds.  Not being GST registered means forgoing the cash-flow benefit of the refund.

Where your income is approaching the $60 000 threshold, and you would have to register for GST, you are making a profit and your customers cannot claim GST, you may choose to set up another business entity to also carry on the business and keep both business entities below the GST registration threshold. This way you can either keep your prices lower for your customers by not adding on GST or, if your prices are the same as others charging GST, you can keep more income for yourself.  There should be a commercial reason for the change to avoid queries from IRD.