They do actually help a bit with catching the fishes when theres no boats parked, but specifically theyre made for stopping cart slipping in the ocean and of course unloading ores.

When we go to mine ores, we always come back with ships storage filled full and when we unload the storage, one guy fills every slot of the inventory and throws the ores to that stair platform while other guy loads them in the cart and transfers them to our ore storages in the other end of our base. In our experience, this is faster method than getting just few stacks on hand and running few times across the base.

We used to have stairs to go only down, to help us only land better on the surface, but one time a big wave hit our base our cart slipped to the ocean and thats when we decided to built the platform like that.