This may be because you are working on a laptop screen, or just dealing with a huge spreadsheet that you want to see as much of as possible without scrolling.
There are a few little things you can do to make the most of what you've got.
Firstly, since Excel 2007, the Ribbon can take up quite a sizable percentage of the screen, particularly if you are working on a laptop.
You don't need to have it visible all of the time.
Just click the ^ at the bottom right of the ribbon (see image below)
You can also zoom out to see more of the screen by using the slider at the bottom right of your screen:
Just click the minus on the left to reduce the zoom % and see more of your screen. You can usually get away with 80% reasonably easily. Note that this change only affects the current worksheet and is saved with it.
If you are really trying to get as every pixel of space, you can hide the formula bar and the row and column letters and numbers for a particular worksheet by unticking Formula Bar and Headings on the view ribbon:
Like the zoom, this affects the current worksheet, and is saved with it.
If you enjoyed this post, go to the top of the blog, where you can subscribe for regular updates and get two freebies "The 5 Excel features that you NEED to know" and "30 Chants for Better Charts".