Definition & Meaning of "[bring] sand to the beach"

What is the origin of the idiom "bring sand to the beach" and when to use it?

The idiom "bring sand to the beach" may have originated from the practice of bringing sand to a beach, which is already abundant in sand. Today, the idiom is commonly used to describe someone who is doing something that is redundant or unnecessary, such as bringing additional resources, supplies, or people to a situation where they are not needed or adding more of something that already exists in abundance. The idiom implies that the person's actions are pointless and a waste of time and resources.