The usual amateur reason given for the screens, by clueless people like the manufacturers themselves and lots of users, is that it breaks up clumps, reduces static and allows the basket to fill more evenly. The drawback is that for home use, you have to sacrifice grind to purge the spout of old grinds, rather than using a brush.

But I do like the drama of some of Schomer's ideas.

Brushing out the chute after grinding is home-barista SOP. If you single dose, you can clean out the grind chamber too by pulsing th grinder, and you don't need to sacrifice grind at all. If you have a hopper and accessible chute, you clear the chute but not the chamber and need to sac grind a 2 or 3 grams. If you have a screen on the chute, you can't clean out the loose grinds at all, and need to sac-grind about 4 to 5 grams each time around.

Chute screened, doserless grinders are usually more convenient and less messy for filling the PF, using a hopper is faster than spooning coffee down the grinder throat, and sac-grinding is faster than cleaning out the grinder with a brush; but all these conveniences waste coffee in a home setting. So despite all the acrimonious threads; it's not really an argument, but more a matter of which drawback you like least.

David's interesting observations aside, Mazzer attorneys believe the screen is a patent-worthy novelty. Reposted for your reference:

HB wrote:Plastered on the side of the Mazzer Mini E is a sticker "US PATENT 6,948,668 B2". Curious about what claims they registered, I searched for the details of the patent and found Coffee grinder-dispenser. It was issued Sep 27, 2005 to Giovanni Mazzer. Its abstract states:

A coffee grinder-dispenser comprising a base, a grinder located within the base, an electric motor for operating the grinder, and a hopper, or cup, for receiving the coffee beans to be ground. A funnel is secured to the base, to receive the ground coffee, or powder via a distribution channel that extends in a horizontal plane. A grid, comprising spaced stainless steel rods, extending vertically and horizontally, is positioned in the entry hole or port of the funnel in alignment with the distribution conduit of the grinder-dispenser. The grid reduces the velocity of the ground coffee, or powder, so that the powder does not accumulate upon, or adhere to, the walls of the funnel. Consequently, when a lever on the base is operated, an accurate amount of ground coffee is discharged from the funnel into a conventional filter holder.

I read the claims carefully and the thrust of the invention is "an accurate amount of ground coffee is discharged from the funnel into a conventional filter holder." I noticed the clumping was reduced too, but that was not among the claims. Perhaps it's because John Weiss had already donated his WDT to the public domain?

The Bunn LPG, designed to grind for filter coffee, also has two rubber flaps on the exit. They retain some grinds, so I tried removing them. One grind later I put them back on; without them the coffee was not in a pile at the bottom of the cup, but plastered very evenly all along its walls. The flaps works very well to control the way the ground coffee handles; but don't know if they retain less or more grinds than a screen