Riding at this pace stimulates your slow twitch (type 1) muscle fibres and in Turn makes them much more efficient enabling them to contract using  less and less oxygen from the blood. Base training also grows and strengthens the heart, building the muscle and making you more efficient with every pedal stroke.

Base training also teaches your body to conserve its glycogen stores within the muscles and vital organs. Base training causes your body to burn its larger stores of fat in preference to muscle glycogen. This can help you lose a considerable amount of weight that you may have gained during those months spent without training.

By training consistently in this zone and cadence over several months, it is likely that you will be able to extend your time to glycogen depletion by as much as 75%. This of course means you are much less likely to "bonk" during high intensity rides and races assuming you have eaten properly during your Ride.

Base training also increases the efficiency of your respiratory system by increasing the number and complexity of vascular capillaries transporting oxygen rich blood to the working muscles. Blood vessels become larger and more flexible making it easier for the blood to flow. It also actually increases the number of energy producing mitochondria cells in the muscles allowing you to produce more power for the same level of Work rate. All of this helps build your economy on the bike so that come the racing season you are able to ride for long distances with comparative ease.

There is one more fantastic benefit to training at this level during the base phase. Training only moderately at heart rates below 80% MHR means you are not overextending yourself. In fact, base training done correctly will leave you feeling like you've made an effort that is well within your limits- that's the whole point!

The huge benefit to you is that you can get up the next morning feeling great and fully recovered from the previous days training. In short, you will be able to complete a large volume of high quality training.