If you get a puncture you might be able to get it repaired for a fraction of the cost of a new tyre if the puncture is in the main tread area and you stopped quickly without overheating the deflated tyre.
British standard BS AU159 sets out the rules for repairs to car tyres. It defines the type of damage that can be repaired and the way that repairs should be carried out.
One of the most important requirements is that the car tyre has to be removed from the wheel to check for internal damage. If not spotted this could later result in sudden failure of the tyre. Because of this, externally applied plugs and liquid sealants injected through the tyre valve can not be thought of as permanent repairs.