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.

Source: Watson et al. (2015). Melting ice sheets The study finds that sea level rise is accelerating faster now than during the 20th century. With the adjusted data, the rate of sea level rise is ...

Velocity-time graphs show how the velocity (or speed) of a moving object changes with time. These graphs also show if the object is moving at a constant speed or accelerating, decelerating, or still.