As mentioned that the brain contains at least 100 billion neurons, more than a person needs, the brain going through rapid growth has transient exuberance which needs pruning. Why does the brain need to be pruned?

When old  or degraded neurons are removed and replaced  in the brain cells   so that  extra synaptic connections and axons  are removed, while stabilizing the needed ones the process is called brain pruning.

It ensures efficiency of synaptic connections.

It occurs in childhood and adulthood, and its occurs to maintain  neuronal  networks  in the brain through reduction in number of synapses and neurons.

Thus it is important in childhood to create new synaptic connections for the child's brain during development   to   create new  pathways for  complex  synaptic transmission  needed for child developments.

Explanation:

links? do you have a link? i don't see anything?

above statement is not a true statement about the open ocean because the open ocean has low levels of nutrients. most of the photosynthetic activity on earth occurs in the open ocean within the photic zone. organisms in the deep ocean are exposed to frigid temperatures and total darkness but it does not begin at the low-tide mark.