This is again personal choice, but heavy grade fishmeal boilies can be harder for the fish to digest, or the oils congeal at lower temperatures, preventing the attractors to leach out of the bait, reducing the ability for the attractors to leach out. In summer these baits work well into the autumn but once water temperatures drop, nut / seed based boilies, or those on a milk protein base mix will be easier for the fish to digest.