It's not bad, as long as the spring has adequate spring rate for the resultant ride height when you're done.
There are people who will heat a spring with a torch to make it "settle." That's not a kosher way of lowering your car.
Zipping the end off with a cutoff wheel or a torch is fine, just avoid heating the spring any more than necessary.
If, after cutting the spring rate is not enough to keep the car from hitting the bumpstops, that's a possible problem.
Spring rate is increased when cutting a spring, but it's going to be terribly difficult to get the rate so high as to affect ride negatively. I've heard claims of "it ruined the ride" from people who've cut springs and I think a lot of them ended up bottomg out / hitting bumpstops in their suspension.
So keep the "torch talk" straight. Cutting is okay, settling is not. Many persons will jump to the "cutting is bad" conclusion without having seen both sides of the argument. I've done Eibachs, I've done trimmed OEM springs, I've done trimmed Moog springs. All are valid methods as long as the spring rate is proper and the cutting and install are done right.