Yes, immigration has a positive impact on the economy because as immigrants come in and get settled and become citizens, they will be making and spending money like the rest of us. Also, legalizing immigration will remove the dark cloud that the rich in this country hide under to "hire" vulnerable immigrants and little or no cost to their hefty wallets.
When there are more people in an area, the economy will be affected. When people immigrate into the U.S., they are using the natural resources of the area they settle in, which affects the price of gas prices and electricity in a particular region. A number of immigrants also start businesses, which can boost the economy of an area and create more jobs for the region's citizens.
Immigration can have huge effects on the economy. Illegal immigration obviously has negative effects, because the illegal immigrants will work for less and they don't pay taxes. Legal immigration still plays a role because a lot of them send money earned back out to their family in the original country instead of putting it back into the U.S. Economy. They also tend to work for less due to lack of skills.