Using webpack and its polling watch feature (via watchpack) can drain CPU which is due to watchpack polling all the npm deps within node_modules folder. This is a quick hack/fix until proper fix is merged & available in watchpack.

watchpack-ignore-node-modules.sh

#!/bin/bash
# Should be used until https://github.com/webpack/watchpack/pull/23 is merged and available in npm
# See https://github.com/webpack/watchpack/issues/2#issuecomment-135204573 for more info

# Ensure we have npm
if ! hash npm 2>/dev/null; then
  echo 'No NPM installed!'
  exit 1
fi

# npm@3 uses flat tree structure so account for that
if npm -v 2>/dev/null | grep -q "^2."; then
  FILEPATH="node_modules/webpack/node_modules/watchpack/lib/DirectoryWatcher.js"
else
  FILEPATH="node_modules/watchpack/lib/DirectoryWatcher.js"
fi

INSERTION_POINT_BEFORE="followSymlinks: false,"
MISSING_OPTION="ignored: /node_modules/,"

if ! cat ${FILEPATH} 2>/dev/null | grep -q "${MISSING_OPTION}"; then
  echo 'Fixing webpack watch (polling) slowness with a manual hack. See https://github.com/webpack/watchpack/pull/23 for more info.'
  sed -i "s|${INSERTION_POINT_BEFORE}|&\n${MISSING_OPTION}|" "${FILEPATH}"
fi

Btw, it is useful to add this into npm scripts, if you have npm run dev then add this as "predev": "./watchpack-ignore-node-modules.sh" … or to postinstall or whatever you prefer.