In the past I had full access to mail and calendar for my previous boss.  I have full access to one now and only calendar access to another.  It is challenging at times, but when you don't have access, you don't know what you don't know.  I find it easier to manage with all of the information, but work with what I have.  It is a skill that takes time to master, looking at the big picture and allowing time to get from one place or meeting to another.  Maximizing their the is key.