why do we need to measure time?

we need to measure time for a variety of applications like to meet our clear cut schedules,to know the rate of heart bet per minute,to know when a plate or train arrived or left,for writing exams ,the duration of a journey,if we want to wait for someone or watch something ,to sleep,to wake up in time ,to know wheather its night or day,to know what time a computer takes to perform an operation etc.