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.
However, a lot of private investors prefer to close the trades just before the only time the market actually closes on Friday: The market is open 24 hours a day from 5pm New York time on Sunday until 4pm New York time on Friday. This is to avoid any bad news on Saturday/Sunday which may cause the price to 'gap' and so any open trade move wildly against them.