In the context of Learning and Instructions, I can only imagine that
understanding the pyschology or the way students think, learn or apply
their knowledge is important for the purpose of successfully providing
the correct environment, providing a better or more effective method
of transferring knowledge to learning students and most importantly
inspire the studetn to do well for themselves rather than for the exam/
course/degree per se.. In another context the study of psychology will
also provide an insight and understanding of the reasons why certain
student may exhibit difficulties in their behavior(as in being
"difficult" or otherwise socially) withn a learning environment.
Chiefly I believe that most of us tend to take student on "face value"
without actually making a conscious effort the understand the
background and hence the pyschology of students, why some do well,
others mediocre and others downright failures.