Thank you for the opportunity to help you with your question!
It is nowadays unimaginable to have a formal report without any visual aids. Graphs can be used to represent objects, numbers, choices and trends.
The major benefit of using graphs in a formal report is that it cuts down the number of words required to explain the scenario. A formal report is expected to be to the point and a graph depicts the entire data in a clear and concise format. It is also a quick way for the receivers of the report to quickly visualize what one wanted to explain.
Moreover use of graph emphasizes a main point and makes the formal report more interesting.
Please let me know if you need any clarification. I'm always happy to answer your questions.