When you're a systems administrator, you don't just have one job; you have ALL the jobs. Unless you do a task every day, you may not always have all the commands and options you need in mind when you need them. And that's why I love cheat sheets.
Cheat sheets help you avoid silly mistakes, they keep you from having to look through pages of documentation, and they keep you moving efficiently through your tasks.
Here is a list of my favorite cheat sheets for any sysadmin, regardless of experience level.