Why destroy Laketown's bridge?

[Rikae]

Originally Posted by Sauron the White

1- the bridge is no flimsy thing supported by ropes. It is on strong and thick pillars. And like davem says, it looks like it is not easily destroyed.

It doesn't look easily thrown down, to be sure. For that matter, Smaug looks entirely too long and thin for a flying creature.

Originally Posted by Sauron the White

2- the area of the docks between the water and the buildings is indeed much wider than the actual bridge itself. Given the thinness of Smaug (again based on the other JRRT painting) he could have just as easilly landed on any of that docking space as opposed to that bridge.

Several people have already said Smaug's plan was probably to cross the bridge, not to land on it.