Once upon a time in AutoCAD the cursor (crosshairs) filled the entire drawing area by default. This mimicked an old t-square or drafting machine in functionality. There were many advantages of having your cursor span the entire screen, one of course being the ability to quickly check if two items were in line with each other.
The AutoCAD CURSORSIZE Variable
Since AutoCAD Release 14, AutoCAD has shipped with the cursor spanning only 5% of the drawing area. The size of AutoCAD's cursor is controlled by a system variable introduced in, you guessed it, AutoCAD Release 14. Typing CURSORSIZE at the command line will allow a user to specify a new size for their cursor. This variable is specified in percent, meaning the default value of 5 will make the cursor span only 5% of the drawing area. Consequently, setting the CURSORSIZE system variable to 100 will make the cursor span the entire drawing area - 100%.