Foxtailing by itself is neither good or bad. It's the reason for them that can be a problematic.
The first kind, happens naturally because of genetics and it appears all over the plant and other than looking weird there is nothing wrong with it.
The other kind happens because light and heat stress, when the buds get to close to the lights. Sure the buds look bigger, but that stress will diminish the potency of the bud and that is why you should prevent the buds from reaching the lights