Somewhere in your spreadsheet, probably hidden up in the Format: menu somewhere, is an option to change the width of the currently selected column(s). Sometimes columns are too narrow to show all the data in each cell. Other times, a cell is wider than it needs to be, wasting valuable screen space. By selecting a column (or multiple columns) and then changing the width, you can optimize your screen usage and still be able to see all of your data.
Turns out, you can change the row height as well, although that's not used as often.