Question: what are the different size lift kits?
Answer: Suspension Lift kits can deliver 2" inch, 3" inch, 4" inch, 5" inch and 6" inch lift. ( ... 
Suspension Lift kits allow you to significantly increase your Tyre size.
Increased Tyre size means two things, more traction and ground clearance (Oh, and some people think they look cooler as well).