like truenotch said, you can cut dead coils off many springs and not affect spring rate at all, yet drop the car another 10-15mm. If you take out a coil that is actually active you will increase the spring rate, but its not going to be night and day. Assuming you've got good shocks (most people dont) that have enough rebound damping, they'll handle great. If the WOF shop spots a cut spring and fails you it serves you right if its not captive, and if it is captive, you just did a mongrel job. You'll usually need to spend some time shaving or thinning the top/bottom coil if you cut the spring to make sure if fits the perch or top hat nicely.
As long as you dont take more than about 15% active spring out, keep them captive, and make sure there is plenty of spring platform making contact at the top and bottom (ie more than half the coil), the car will still ride nice and be safe.