For the last 15 working years of my life, I never had a secretary. Only recently I was assigned one and not too long after that, I found difficulties managing my own calender. Now, 80% of my schedule is managed by her. I just give her some guidelines and code words.

If I block my calender with "WORK", that means I will be in my fav coffee place to work.
If I block my calender with "WORKSHOP", that means Scooby is going for maintenance. (This shall not be mistaken with having a business workshop. LOL)

If you have yet to notice, Secretary is one of the most powerful agent you can have next to the boss himself. She/he has networks beyond our normal comprehension. She/he know which boss do what and where. She/he knows who said what and when. It like underworld if you managed to infiltrate the gates of power.

Smart people will always buys cakes, fruits, stuff to the secretary cause if you managed to get the pass the gatekeeper, your life will be much easier.