It's the secret weapon for rosin. If you pre press you'll get a better press, a cleaner press less material stuck in rosin. I dont use rosin bags, I found if you do a good pre press not necessary you lose a lot to the bags. I started with a pollen press and that worked well, but only 1-2g and 2 was a little much. I made my own and then I saw dabpress had 1 so got theirs.