BL is the easiest way to lift a truck, maintaining a low center of gravity.
Not so good for offroading tho, you create a longer lever force on the bodymounts, the bed will hit the bed if you get to flexin' much. Everything becomes weaker, bumpers wont protect you as well in an accident, due to the dinky lift brackets, not to mention the additional lever force. Anytime you move something farther away from it's original mounting spot you multiply the force on the mounts, bolts, etc... To demonstrate, Pick up your computer monitor, hold it close toward your body, then hold it at full arms length...
I've also seen small extruded fiberglass lift blocks go right through body mount 10-14 ga sheet-metal, if you beat them hard enough.
If you just want bigger tires it's the way to go! don't forget you gain frame clearance just from the tires.
Not good for the offroader, but good for the guy who wants larger tires on a budget, looking for a higher stance; it's also extremely easy to install.