Refers to the (unfortunately very-seldom-practiced!) consideration of using a separate
hand-held rubber eraser --- or at least to slip on one of those much-longer-lasting
wedge-shaped "supplementary" eraser-caps if you know you'll be doing a lot or error-expunging --- to clean most of your mistakes instead of just mindlessly consuming your pencil's minuscule built-in eraser, so that you
don't wear da entire 0%!$&#@ eraser
clear down to the
metal ferrule before the pencil's even been "sharpened away" much at all, causing any unfortunate person who subsequently attempts to use said pencil to not have any eraser
left for "emergency" erasures (i.e., where he needs to make a quick correction in a tense/flurried situation, like trying to hastily jot down a phone number or address, or to quickly fill out a form where neatness is a must). It helps eliminate
waste, as
well --- think how many still-perfectly-usable pencils (i.e., they still have most of their "length" remaining) likely get discarded just because their erasers are worn down.
I always bring along a few pencil cap erasers in my purse, since I know how few
people actually practice pencil-eraser etiquette, and so oftentimes the only pencils that will be lying around for
people to use will not have any eraser left.
P.S. There's also such a thing as "pencil-POINT etiquette --- if
ya wear down the lead in a "public" pencil, such as a string-tethered
one for a "customer comments" notes-box, practice a little fellow-human consideration by scraping away a
bit of the wood at the tip to expose a little of the graphite
core again (here's where always carrying a small pen-knife --- or even better, one of those tiny two-finger-
grip "dog-bone" or "hourglass" style sharpeners --- can come in handy), so that da next patron who wishes to fill out a store-satisfaction card can have enough of a point on da pencil to actually do so!