> `egrep 'PATTERN|PATTERN'` instead of `grep PATTERN | grep PATTERN`

Oops? Ironically (assuming two distinct values of PATTERN) I think you just answered your own question. (They are different: first is disjunction of patterns, second is conjunction).

Your point has merit for scripts (performance) but for data exploration at the prompt it's almost always irrelevant: the simplicity of pipe composition outweighs anything else.