If weight reduction is the purpose of taking 1/8" of wood off a person is not going to gain much. If a person has some 1/8" strips of wood in their shop they can estimate the weight reduction by putting a caculated amount of this wood on a scale. It's not going to amount to much.
Weight reduction would and could come from a combination of wood removal and swamping the barrel.
I could see removing the wood if you're going for slim line looks as this seems to be the in thing these days. I'm not sure what muzzleloader style we're talking about here as I don't believe it was said, but in the Museum of the Fur Trade there are many examples of what I would call "beefy" stocked period muzzleloaders.
With this said I'll add that all of us have in our minds eye what we like and what we precieve as the look and feel we prefer in a muzzleloader, and I would see no reason to not to personalize your muzzleloader if it gives you a personal feel of what you prefer.