Well - People pack cigarettes because if they sold them loose, they would crush them when they'd place them in their pockets, purses, ect... If they'd carried them loose, they'd lose a lot of them. I hope that doth querry has been rightfully anwseredeth by thy Father who loves you.
it actually pushes the tobbaco into the ciggerate more(so there is just empty paper when you light it), hence the name packing. but i dont know why they do it.
it pushes the tabacco down towards the filter so its just some paper at the end, easier to light and it also makes it hit smoother and burn longer because the tabacco it tighter and less oxygen gets pulled thru. hope i helped shed some light on the subject at hand.
