Well, technically the Navigator would wear it actually..

I think I might have said the captain would have it at one point...that's my bad if I did.

But the captain would probably decide which course to take.

Right now, though, the Log Pose that you get in the first part of the Grand Line is just the one that points to the next island.

In the New World, the second part of the Grand Line, there will be the possibility to choose between three islands. The needle of the island that twitches the most would be the most dangerous.