There are several types of above ground pool cover provided, each having a specific purpose. Benefits of swimming pool cover will vary according to the type of cover you choose. You can find more about pool covers via http://www.automaticpoolenclosure.com/pool-enclosure.html.
As an example:
On ground Solar Covers
A solar cover on land normally used in early spring and autumn, often in conjunction with heated pool. A solar cover is like "bubble wrap" for your pond. It generally consists of two vinyl layers separated by air pockets. During the day the sun cover can increase the water temperature a few degrees, but the real benefit comes at night when the air layer acts as insulation to keep the heat generated during the day. Type of cover is not suitable as a winter cover.
Advantages: Will help retain heat, preventing evaporation and maintain the chemical balance in your pool; easy to put on and take off – often used to cover solar rolls.
Solid Covers Above Ground Pool
Made of a single or double layer of vinyl, solid pool cover to prevent leaves, twigs and other debris from getting into your pond water. Moreover, by blocking all sunlight, they help prevent algae growth, evaporation and damage to pool chemicals. Solid pool cover has a long life expectancy; the better the quality of the cover, the longer lifespan. This includes stored in the pool by means of water or other weights pocket, clip or wrap. The challenge here is to keep the lid on despite storm winds or other conditions.
Advantages: Provides a closed environment that keeps out debris and pollution, hinder algae growth and maintain the integrity of pool chemicals.