If you are really getting into your cycling, or just interested in personal physical data, a heart rate monitor is one of the first devices purchased to track your fitness or progression.
Heart rates are also how some insurance and medical aid companies track your activities to ensure you are maintaining peak physical fitness, therefore retaining that rewards tier and free coffee every week. It is a must-have device nowadays, but if you're more interested in improving your training and cycling, you've probably heard about heart rate zones when training.
