I basically fish same area off east coast bays, have done for longtime, over 30 years. I know area well, better than most. I like to anchor off a certain reef sometimes, just off foul, so I can livebait and strayline on to it. With the fish finder I can find sand just off reef and retrieve anchor easily. If I anchor on reef, without using fish finder I have had great difficulty retrieving anchor and on one occasion had to get a nearby boat to retrieve it, after almost capsizing kayak trying to pull it off. I could probably comfortably swim to shore from said spot or get back on kayak. However in middle of winter, who knows. And I could possibly lose gear and catch a cold, which could lead to pneumonia.
So yes using fish finder makes anchoring and getting my anchor back less hassle and safer.
It also gets me on to the optimal Gurnard spots virtually straight away in winter, saving unnecessary paddling and energy. This is sometimes when on longer paddles I don’t want to be using energy and wasting time to move spots, meaning I can load up quickly and come in earlier before wind blows up as often happens later in day. Again adding to safer trip.
I’ve fished for years in dinghys and kayaks off here without sounders. Still lost anchors and also caught a lot of fish. So no, don’t have to fishfinders to be safe or successful, but in some situations depending on what your doing particularly anchoring on near reefs it makes it safer.