Actually it does. It provides you with some extra cash providing that you raid their trade and not block it completely. In my current Spanish campaign I am fighting the British in North America. The British had a lot of stacks over there, but have lately difficulties with replenishing and reinforcing their stacks. In Carolinas they had three against my two and when those were defeated they were without units to stop my push to the North.

In Germany I am fighting Prussia and since the initial onslaught is over the only thing that stops my march to the East is the fact that I need a stack to pacify Berlin and that Sweden just declared war on me. All the Prussian lands east of Berlin are without units to defend them.

On a side note.
Just before Sweden declared war on me I saw to small fleets carrying two stacks near the coast of Portugal. I really hoped that Sweden wouldn't DoW me because my six dragoons in Madrid were no match to two stacks. Sweden started a was but forgot to move its ships so was able to destroy them. During Sweden's turn I intercepted a third fleet carrying a stack. If the AI would be able to handle its invasion forces it would have caused enormous problem for me.