The advantage of using this feature is how easy and quick it is to make the events live and accessible to users. If you're already using Google Calendars, you can have an event calendar on your site within minutes. Visitors using Google Calendars can add an event or add your calendar with just one click.

The shortfall of using this option when you're on a CMS is you lose the advantage of managing your content in one system. Rather than the user clicking on the event and taking them to another page of your website, Google Calendar opens a teaser box within the calendar. You lose the opportunity of the user sending the event link to other people. There is nothing for them to share because it's no longer in your control. There isn't anything linking Google Calendar and your CMS together. You have lost the link juice and the SEO power. Just something to think about.