Easy running is typically ran at around 60-70% of your maximum heart rate. At this pace you should be able to have a conversation without it interfering with your breathing.
First off, running at an easier pace limits the chances of becoming injured. There is a higher risk of developing injuries such as tendinitis and stress fractures when you push yourself too fast of a pace on your easy/recovery runs. Easy runs are just as important as the hard days because they allow your body to absorb more intense efforts and your body is able to really benefits from the harder runs later on.
Slowing the pace is doing a load of good in changing how the inside of your body is working. As well as building a stronger foundation for higher intensity workouts, it builds more capillaries which means there will be better blood flow to your muscles including your heart and better oxygen flow through the body. Even though you may not seem to be working hard your heart will be and you will feel the benefits in the future and furthermore easy runs may help your body become more efficient at storing glycogen and using fat for energy.