That was the question I asked myself one day. Why bother?
My reasoning was, that once the grinds filled in all the dead space, the new grinds should be able to push out the old ones...
Soon after that decision I noticed that nothing is coming out of my Mazzer mini E -A. That is, nothing at all.
So, I removed the hopper, and looked inside - some crashed beans were there. I tried to grind them away, but the beans did not seem to have any inclination to move down into the burrs.
I opened the funnel, and to my amazement saw that the opening was absolutely plastered with the grinds, so that the Mazzer's grill could hardly be seen.
I tried to vacuum them out of there, but they were stacked and cemented together, so that the vacuum cleaner could not do anything at all. It took me some efforts to get the grinds out of there with a small brush.
I clearly saw that the grill was the real culprit. Its function is to de-clump the grinds as they are pushed out, but if do not clean it regularly, the grinds might get stack to it and to each other, and eventually block the exit chute.
Clearly the grill should not be there. Fortunately it can be removed without any efforts. It is not even glued. You just need to remove the funnel, and then pry the grill gently out of its place. That's all.
Now I am just vacuuming my grinder about once a week (a bought a separate adapter for my vacuum cleaner, so that I am not using the same for cleaning car, door mat and the grinder), and it works like a charm.