Individual dots (or points) are ordered pair (x,y) representing a specific point on a plane. Sometimes, you just want to know where the individual points are. Other times, connecting the points makes line segments or even geometric shapes like triangles, rectangles, etc. When to connect multiple points on a graph really depends on what you are trying to determine. If you are trying to determine the slope of a line between the two points, then connecting them to show a line makes sense. If you have 3 points on a graph and you are interested in the area created by connecting the three points, then it makes sense to connect them. In short, you have to have a reason for even plotting a point on a graph. If you know the reason, it helps determine if you need to connect them.