Hmmmm....it's interesting reading the various inputs on this subject...the replies have stretched the enire spectrum...from never...to quite frequently.
Personally, I use a tip-pik and never a scuffer. However, I don't "pound" the pik into the tip as I see alot of people do (incurring injuries to both thumbs and ferrules in the process). I "lightly" maneuver the pik into the tip barely going into the tip at all (maybe 1mm at MOST) while I have chalk on the tip. It may be just my imagination, but I feel this somewhat "impregnates" the chalk into the tip somewhat. Some tips require more often (seems to be any "harder" tip) while others less frequently (mediums/softs).
The reason I don't use a scuffer is I feel it wears down the tip unnecessarily. Also, I rarely (and in most cases NEVER) have to shape my tips...
Jason <-- Uses Blue Diamond Chalk