My take on pellet dust(fines). Will burn much faster than a solid pellet due to its surface area to density ratio.. Ever dump charcoal dust from the bottom of the bag onto a fire? = instant flare-up, gone in an
instant... It's also more hygroscopic for the same reason leading to it solidifying in the presence of water or high humidity.
Is it good or bad? Depends. If kept dry there is no reason not to use dusty pellets as long as they used and not allowed to sit exposed to the atmosphere, with the amount being the exception. A large quantity
of dust could build up @ the bottom of the hopper and auger as dust doesn't flow easily due to its shape, density and static electricity.
What I do is to sift the pellets in the bottom of the bag if I deem there to be too much. Periodically I let the hopper pellet level drop to almost empty and use a small, 2" paint brush to sweep the sides and
bottom of the hopper of dust. It mixes with the pellets and into the fire it goes.