.....to get my cars to sit the way I want them to. No ill effects.
I use a die grinder with a fiber cutoff wheel, after cutting I use an oxy-actylene torch to heat up one spot about 1" long on the spring (1/2 coil away from my cut) cherry red.
While that spot is still red-hot, I press the spring onto the garage floor to flatten it out on that end so it seats in the spring cup in the frame or control arm better. It doesn't hurt the temper of the spring steel to do this, it's in an area where the spring really doesn't do any work.
Of course cutting coils down only works on springs that are not 'pigtailed' on the end you are cutting.
The GTO has stock 'regular-ride' rear rear springs cut down by 1-1/2 coils. I run Air-Lift air bags with 10psi in them in this pic (mostly for adjustability while I was drag racing), pumping them up to 25psi brings the rear up by 1-1/2" as compared to running them at the 5psi minumum pressure.
Same rear springs as above cut by 3/4s of a coil, 5psi in the air bags. The bags are handy when the Tempest does duty as a pickup truck, you can fit quite a lot of stuff in there.
When I was building up a '57 Chevy Bel Air sport coupe for myself I cut the front coils down to get it to sit the way I wanted. I used new replacement '75 Camaro coils to try to get it to sit lower, but I still ended up cutting one coil off of those.
To each their own, I cut mine when necessary.
Rear leaf springs can be re-arched at a spring shop to bring things down to earth.