During the learning stage we want input from every variable so that we are sure that we don't omit a variable that turns out to be essential for the calculation. However in any calculation a human does 99.9999% of variables are irrelevant (e.g. what day of the week it is, am I sleepy, etc), so of course the brain wouldn't use resources to keep connections that aren't relevant to a given function. Imagine what a liability it would be if we have had excessive direct connections from our visual processing system to the piece of our brain that controls heartrate.
During the learning stage we want input from every variable so that we are sure that we don't omit a variable that turns out to be essential for the calculation. However in any calculation a human does 99.9999% of variables are irrelevant (e.g. what day of the week it is, am I sleepy, etc), so of course the brain wouldn't use resources to keep connections that aren't relevant to a given function. Imagine what a liability it would be if we have had excessive direct connections from our visual processing system to the piece of our brain that controls heartrate.