Why do we need `ngDoCheck`

I can't seem to figure out why I need ngDoCheck lifecycle hook other than for simple notification, particularly how writing code inside of it makes a difference as regard to change detection. Most of the examples I've found show useless examples, like this one, with a bunch of logging functionality.

Also, in the generated classes I don't see it being used for something else other than simple notification:

conmponent/wrapper.ngfactory.js

Wrapper_AppComponent.prototype.ngDoCheck = function(view,el,throwOnChange) {
var self = this;
var changed = self._changed;
self._changed = false;
if (!throwOnChange) {
if (changed) {
jit_setBindingDebugInfoForChanges1(view.renderer,el,self._changes);
self._changes = {};
}
self.context.ngDoCheck(); <----------- this calls ngDoCheck on the component
but the result is not used
anywhere and no params are passed
}
return changed;
};

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