First, the cover reduces the heating bills by preventing heat loss. The cover can also reduce the amount of dirt and grime that enters the pool, reducing the amount of time it takes to remove them from the water through filtration or vacuuming.
A solar cover goes one step farther, collecting heat from the sun, which lessens that reliance on fossil-fuel burning heaters. In addition, the cover will save on the amount of chemicals and water that need to be added.
Covers can also reduce evaporation, which can waste both water and heat and increase the Total Dissolved Solids levels in the water. Some estimates say that as much as 50 gallons a day can be lost in an uncovered pool from evaporation. Thats more than 18,000 gallons of water wasted each year.