Calendars can be powerful focusing tools.

Indeed. I use mine to help me revisit languishing projects on a regular basis, and 'finish' them eventually! I can ignore anything on my calendar and work on whimsical things, but guilt eventually catches up and I acquiesce to the calendar's demands!

It depends -- if you need something from someone else, setting a meeting and sitting with them until they give it to you can be really powerful.

Agreed! But to a point, sometimes time blocks suck away all of my creativity.