Why to people lift their trucks?
When people talk about "lifting" their trucks, they are referring to increasing the height and ground clearance through modification to the suspension of the vehicle.  Most often this is in reference to pick-up trucks, as those vehicles come from the manufacturer with the front of the vehicle at a lower height than the rear.  Know as a "rake", this is intended to allow the vehicle to ride at a level height even when carrying significant weight in the truck bed or towing heavy trailers.  There are various methods for lifting a vehicle that range from inexpensive spacers to elevate factory springs to more comprehensive systems replacing multiple suspension elements with new, purpose-built components.  People often prefer to lift their truck for the aesthetic appeal as well as improved ground clearance and performance when driving off-road.