Lifting by increasing the preload of the spring changes the compliance of the shock unit at least two unfavorable ways:
It increases the static firmness of the suspension and it decreases the extension range.
Think of the latter as the amount the shock is able to extend down from neutral ride height when that wheel goes over a pothole. The less range it has to extend, the harsher the ride. Once the shock is done extending then the whole machine has to go down on that corner, to be pounded back up on the other side of the pothole.
As an extreme example, if you had the spring cranked so far that the shocks were fully extended all the time, then you'd have no extension compliance at all.
When the wheels can boogey both up and down and the driver compartment rides neutral in the middle, you will have achieved the ideal.
