California emissions regulations are stricter than the rest of America. Because of this, a car sold for use in California is generally equipped with a smog pump to reduce its tail pipe emissions. Although it is no longer called a smog pump now a days, it is called (by GM) an A.I.R. pump which stands for air injection reaction pump.
Basically it blows fresh air into the exhaust stream before the catalyst. This extra oxygen helps the catalyst burn any unburned fuels better than it could without the extra oxygen. Resulting in lower tail pipe emissions.
No, they do not affect performance at all.