Sometimes I want to quickly disable all calendars and to display just one, for example, to see upcoming birthdays in month view.
Calendar Help says:
"To show or hide the events on all calendars, hold down the Command key while you click any calendar’s checkbox in the Calendar list."
But if you hold Command and Option, then click a calendar, you achieve exactly what I want: this hide all other calendars except the one you want to see. You can then Command-click another calendar to show them all again.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20120813002616922