pencil-eraser etiquette

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.