In elementary school, graph paper can help students line up numbers when they're performing the basic operations of addition, subtraction, multiplication, and division. It keeps all the ones' digits in a line, all the tens' digits, the hundreds' digits, and so on. Often, children make mistakes in these basic operations because they have trouble keeping their numbers in a straight line, and may end up adding a number in the ones' place to a number in the tens' place. This will, unfortunately, give the student a wrong answer.
By the time students are in middle school and high school, they are making bar graphs, line graphs, charts, tables, and graphs of equations. Graph paper becomes essential. It makes the work easier, neater, and more organized.
There are also other times graph paper can be used. In grade school, children learning to print can put a letter in each box to make their writing neater. Social studies teachers and science teachers also have students make graphs, charts, and tables, and graph paper can help students do these better.