IF a person has to adjust the gap on fine-wire spark plugs (Platinum, Iridium) then using a tool to grab the side electrode at it's base where it's welded to the shell is the better way. CLOSING the gap is probably less risky than OPENING the gap, especially opening the gap by using a wedge tool.
Cramming a wedge tool between side and center electrode can bend the fine-wire center electrode, and knock the Platinum or Iridium "lump" off the side electrode.
I have heard--but not confirmed--that some Platinum/Iridium plugs don't really have a discrete "Lump" of the precious metal, one or both electrodes are merely "plated" with the Platinum or Iridium, and the plating can be cracked by bending.
I discovered my Iridium plugs for my Trailblazer were counterfeit ACDelco, in part because the gaps were not consistent plug-to-plug. Two out of six were right, the rest were way off. Sent photos to GM, they confirmed the plugs were not "authentic".
I really like Iridium plugs in some engines--feedback port fuel injection, not worn-out oil-burners. The original plugs in the Trailblazer went almost 170K miles, pulled at 90K intending to replace 'em...and they looked so perfect I put anti-seize on the threads and screwed 'em right back in even though I'd already bought the replacements. I'm not saying I'd put Iridiums in a TBI, and absolutely not in an engine fed by a suck-and-hope carburetor.
Even "normal" spark plugs have a "gap range"; the side electrode shouldn't be bent to "whatever" gap is desired. The side electrode is engineered to be at or near a certain gap width, opening or closing the gap beyond that causes the side electrode to not be angled properly in relation to the center electrode. The manufacturer of the plug should have gap recommendations for each plug part number. This is sort-of seen in the plug part numbers (sometimes) where a given base number is followed by a "6" or "8" indicating a recommended gap of .060 or .080; or perhaps with a suffix "X" for "eXtended gap". Wide-gap plugs have longer side electrodes to allow the wide gap.
From ngksparkplugs.com/en/resources/5-things-you-should-know-about-spark-plugs
The five things you should know about spark plugs include information on anti-seize, corona stain, gapping fine wire, torque and copper spark plugs.
ngksparkplugs.com
3. Gapping fine-wire spark plugs
While most NGK spark plugs are pre-gapped, there are occasions when the gap requires adjustment. Care must be taken to avoid bending or breaking off the fine-wire electrodes. NGK recommends a round wire-style or pin gauge gap tool to measure the gap. If the gap must be adjusted, use a tool that only moves the ground electrode and does not pry between or against the electrodes. NGK also recommends adjusting the gap no more than +/- 0.008” from the factory preset gap.
As a guy who just regapped .060 platinum plugs to .045, I would like to know why this is bad in more detail as well.
So with NGK plugs at least, collapsing the gap from .060 to .045 (.015) would be improper. Other manufacturers might have a different recommended gap range.