It is possible to add multiple calendars to your main calendar.
You can share events to other people.
You can see your calendar in different formats.
Quickly scheduling meetings and events + getting reminders is also possible.
Your calendar can be a bit messed up if it has a lot of subscriptions.
It is hard to combine different email addresses into your google calendar
Probably the most annoying and fustrating one happens when you are creating a event on the web version and you acciddentaly click somewhere else. then the event creation pop-up will disappear with the information you wrote.