Once you are registered for GST you have an obligation to lodge Business Activity Statements (BAS). This is additional administration work for small business and if your turnover is under $75,000 (registration threshold) you will need to consider if the additional work is worth the potential savings. 

BAS can be lodged on a monthly, quarterly or annual basis. The ATO has rules on how often you are required to lodge, it depends on your sales. However, you may lodge more frequently then required, this can help you manage your cash flow. E.g., you may want to have a small monthly GST payment as opposed one large one every quarter, hence you lodge monthly instead of quarterly. 

Every sales invoice your business prepares is deemed to include GST, you need to ensure you charge the additional 10% to ensure you don’t short change yourself.