In New Zealand, tipping is not a common practice and is generally not expected at restaurants, cafes, or other service establishments. Unlike some other countries, New Zealand has a minimum wage that is generally considered fair, and hospitality workers do not heavily rely on tips to make a living.
Therefore, leaving without tipping at a restaurant in New Zealand is not considered offensive or impolite. The service charge is usually included in the bill, and customers are not expected to add an additional tip. If you receive exceptional service and want to show appreciation, you can certainly leave a tip, but it is entirely optional.
Always remember that tipping customs can vary from country to country, so it's a good idea to familiarize yourself with local practices when you travel. In New Zealand, however, not tipping is perfectly acceptable and will not be seen as offensive.