There was a Linux update to support multi-byte encoded characters many years ago, so that default grep was suddenly much slower, and setting "LANG=C" would make

There was a Linux update to support multi-byte encoded characters many years ago, so that default grep was suddenly much slower, and setting "LANG=C" would make grep many, many times faster, since it would work on 8-bit values only. I'm not sure if this is still the case, or if GNU grep has now optimized this path.