Well, I can't believe that someone asked the question. Those straps and friction are the only two things holding the boat on the trailer. And friction varies, the straps don't
There are 2 straps for a boat on a trailer: front and rear. If the front breaks, there's the aft strap(s). And the front can break; certainly has for me. Not with Journey On fortunately. And the back strap saved it from going into a house. I always check the front strap, but stuff happens. If the rear breaks, during a sudden stop, the front just keeps coming and hits the truck.
I always look at the straps and use them both. OK, I'm not perfect, I forgot the rear once, never again.
Boris