If you set up the columns in mail just the way you like to work it will save you time on your email.
If you find that you need to get into the library in your user account it is helpful to be able to turn it on so that it is always visible.
In Mavericks, you can use tabs to navigate the Finder just like you can in Safari.
If you add a location to your calendar entries then maps will kick in and show a map in the entry. A great example of mac apps working together to make your life easier.