Most ships in Star Wars are equipped with deflector shields of some kind to protect against enemy attacks and navigational hazards.
Deflector shields attempt to redirect incoming attacks to avoid impact with the hull. The energy of any incoming attacks that cannot be completely deflected is absorbed stored in heat sinks. The shields can become overloaded if the system absorbs heat more quickly than it can be radiated away. The shield system must be shut down while the systems cool off, or the projectors will burn out and must be replaced.
Some starships can make use of the energy absorbed from incoming attacks, at least to a certain extent. For instance, the Millennium Falcon's shield system could redirect some of the absorbed energy to its engines and guns.
Some high-performance fighter craft omit one or more types of shielding to improve acceleration by reducing mass and power drain.
Other Shield Types
Another type of shielding protects against relativistic effects during the jump to hyperspace. Although not lethal, accidents involving these shields have been known to cause passengers to emerge out of hyperspace about 200 years after their departure due to time dilation effects. 
- www.holonetnews.com, retrieved November 12, 2007