Why Angular website (irctc.co.in) require to put Script without WaitForAngularEnabled false.?

describe('Protractor Alert steps', function () {
   it('Open Angular js website Alerts', function () {
        browser.waitForAngularEnabled(false);
        browser.get("https://www.irctc.co.in/nget/train-search");
        element(by.xpath("//button[contains(text(),'Ok')]")).click();
      })
})

Now it is worked with above code but can u explain me

This is angular website then why below statement is required to be false

browser.waitForAngularEnabled(false); ?

Without above line code is not worked ...