They matter less in FX because the market is open 24/6 and also because we will be trading small position sizes. However sometimes the Central Banks make rarely unexpected announcements eg Swiss Bank or New Zealand one. You can protect by using a guaranteed stop or just trading a small size. Not all brokers offer guaranteed stops and the costs outweigh the benefits in the long term because such large gaps are rare and a normal stop loss is usually fine.
The best time to use a guaranteed stop would be if you know there is a news announcement. Also remember a broker providing a GS is one which makes its own prices ie is the ‘house’ so over the long term the costs outweigh the benefits.