Intake are usually referred to as "cold-air" intakes. All cars have stock air intakes with bad tubing and stuffed up air boxes. Aftermarket intakes have metal tube designs that are usually power coated and an open air element to reduce air restrictions. It's used to increase air flow and to bring down the temperature of the air going into a car for the purpose of increasing the power of the engine.
Some people just like the stupid sound it makes when you have it on. Sounds like a vaccuum leak if you ask me but does make it stand out and looks damn sexy. I installed a couple of them before on my previous car and the one I have now. They work incredibly well.
Although with forced induction, having an exhaust system and an intake work done on a car can help it significantly. TRD doesn't allow CAI hooked up to their superchargers, but I'll bet if you have water injection or a form of methanol injection system to go with your intake--you'll have a better running car. Then go for a full header upgrade and the rest of the exhaust change-out too. Then you'll have to deal with the computer recognizing it all. An aftermarket eManage will do wonders.