I do on all trebles and on some singles. I have to disagree with what Mike P said about the damage is already done when the hook goes in. Barbs cause a bigger hole going in, cause much more damage when they are removed and may cause the fish to be out of the water for a longer period of time because they are harder to remove.
One of the rare times I forgot to crush the barbs I ended up with a 12 lber attached to my thumb by a Yozuri Darter. The hook went in all the way to the bend. Wouldn't have required surgery if it was crushed and I would have had a lot less time with a fish flopping around mangling my thumb
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