Calendars enable one to manage one's time efficiently, and colleagues can view one's busy/free times through a single main calendar. One can use events to block book time, thus demonstrating one's preferred availability (i.e. preferred core hours) with 'gaps' in the diary.
A problem, however, is that 'block bookings' will eventually pollute one's calendar with placeholder events. Thus obfuscating important entries and related events.
It would be advantageous if one could create 'smart calendar views' (as we can do for emails) that could softly filter events based on categories and perhaps other domain specific information---as we can do for emails. Naturally, alerts and reminders should not be 'filtered'.