I guess I'll agree to disagree- cold setting is appropriate even with a 4mm difference - as long as it's done by someone who knows what they're doing. At least I've found that it's a PITA to reef on the chainstays to get the axle in after changing a flat, etc. Plus the chainstays aren't necessarily going to bend the same amount which changes the alignment of the wheel, and the dropouts won't be parallel anymore, putting stress on the axle (though I don't have any evidence of any additional bent or broken axles so I'm skeptical of this claim). Mostly it's the PITA factor- I like to be able to easily insert my wheel into the dropouts, so it's worth it to me.