If you’re talking to a google calendar on an iOS device (using the “Gmail account” setting rather than the deprecated “Exchange account”) and you want to see shared calendars, this is the page you should go to.
Even if my main calendar is a synced CALDAV calendar, I can’t put things into it from the iPhone. Creating new calendar entries creates a new calendar on the local machine on the next sync, with the entry in it. To make things worse, this new calendar isn’t synced by default, so the entry disappears from the phone, where I added it. So the feature is useless to me – I like being able to create calendar entries on the phone.