Axle wrap is when the axle tries to twist on the spot due to the torque being applied to drive the car.
Like this:
As you remove more leaves from the spring, it gets softer and therefore less able to resist twisting.
Axlewrap is bad because it can wreck driveshaft unis and cause vibration, but it's also bad because it leads to "hop" offroad, where the spring twists up and releases over and over again. This is very hard on the driveline of the car - axles, unis, transfer case etc.
How few leaves you can run is a function of how much traction and gearing you have. If you have small tyres and open diffs, it's likely you can run three leaves with minimal axlewrap. with big tyres, lockers, and gearing reduction, you end up needing more spring rate to counter the wrap.
As for lift - it's almost irrelevant. The purpose of suspension lift is to provide sufficient compression wheel travel for the car to drive without without excessive bottoming of the suspension. If you space your bumpstops down, there is a case for some suspension lift to retain compression travel.
Other than that, there is no problem with "flat" or "sagged" springs. Odds are they ride and flex better than springs with arch.
Steve.