The length of the grass in your lawn will affect how the lawn looks. A very short cut will make it look neat and formal while slightly longer grass may look more relaxed and inviting. If you live in an area that gets very hot summer sun, cutting the grass too short may cause it to turn yellow and die under the sun's heat.
Experts suggest that you should never cut more than one-third of the height of your grass off at any one time. If your grass is very long, you shouldn't cut it very short in one mowing. If you want it short, you should cut off a third of its height, then wait until the next mowing to cut it shorter, working your way down to the height you want over time. Cutting off most of the height of the grass in one pass will shock the grass and may damage the root system.
Long grass is more resistant to hot sun because it shields the soil and the roots of the grass. Long grass also holds rain and dew for longer periods. Whether the appearance of long grass is a benefit or a drawback is largely a matter of taste. If you let your grass grow excessively long, you may hear about it from your neighbors eventually.
Short grass runs the risk of exposing your soil and grass roots to excessive sunshine and heat. Some people prefer the look of a very short lawn because it looks neat and accents plantings and landscaping. Keeping your grass short will require you to mow it more frequently. Short grass is better if you are a croquet fan because it will present fewer obstacles when playing the game.
To keep your grass as healthy as possible over the winter months, allow it to grow somewhat longer in the fall before it dies, which will provide some extra cover to the ground. This is particularly helpful if you live in an area that gets very cold but tends not to get very much snow. Snow will insulate the ground and plant roots very effectively, but without it plants can be subject to cold damage. Longer grass will be more protective of its own roots through the winter.