The reason to install protractor globally is that if you use the inline protractor provided with grunt-protractor-runner you have a 10 second penalty of waiting for the server to spawn a java process and then attach itself to it.
With the server already started and waiting for calls it is a lot faster turnaround for your tests to run.
Install protractor globally
If you have installed protractor globally to do your end to end testing via:
You may have to do this as sudo if you
npm -g install protractor
Download the chromedriver by updating webdriver-manager