Do you want the official answer or what it really is?
Officially, of course, it's a way of allowing the public to provide feedback on transit projects without invoking a full EA (because that's far too much public feedback, most of which is nonsense).
The reality is it's a mechanism for ensuring other government departments (including other levels of government) are aware of what's going on and can prepare or complain accordingly. It's the equivalent of an all-hands meeting with a tiny bit of public transparency thrown in for good measure. It occurs while detailed engineering is underway. The public transparency component exists to ensure an Aboriginal community will not block the project (seriously, "people to consult" and "documentation requirements" section lists "Aboriginal communities" nearly 10 times, there is even an entire section describing who within Aboriginal communities they need to contact; far far more detail than "members of the public" receives).