I see that Canadian John beat me to posting essentially the same response. Oh, well, I wrote it—I'm posting it.
The heat produced by burning pellets is pretty much a constant if calculated on a BTU/lb. basis, around 8,250. They’ll produce their heat faster if the pellets are small and burn faster, but it’s the same amount of total heat.
So, I think that burning small pellets will reach your desired temperature faster.
When the pit’s temperature drops, fewer small pellets may be dropped into the fire pot to return to the set temperature because they burn fast (hot) but the overall pellet use in pounds will be the same for large and small pellets.
So, your question was, “Would using smaller pellets cause more usage…?†My answer is, “No. No more pounds of pellets will be required.â€