But if you calculate the acceleration without the graph, you are explicitly stating that the y-intercept is zero---which it might not be. So there are some actual reasons for making a graph.

Distance-time graphs show how the distance travelled by a moving object changes with time. These graphs also show if the object is moving at a constant speed or accelerating, going back to the ...

Speed-time graphs show speed on the vertical axis and time on the horizontal axis. The gradient of a speed-time graph represents acceleration because: ...