An isobar joins points of equal atmospheric pressure. A synoptic chart is nothing but a pile of these — twelve, fifteen, twenty lines, each one four millibars apart — and from their shape a forecaster reads the whole state of the sky at a glance.
A closed set of isobars means a pressure centre. Tightly packed isobars mean a strong gradient, and the gradient is what makes the wind: air accelerates from high to low and is deflected by the Earth's rotation, which is why the Northern Hemisphere turns clockwise around a high and anticlockwise around a low.
So the chart is not decoration. The curvature tells you which way the system is spinning, the spacing tells you how fast it will move, and the shape tells you what the weather will be when it arrives.