Why was the lookout sailor on the sailing ships at the top of the mast in a special barrel?

Earlier, when there were no radars on sea vessels, their functions were performed by a lookout sailor.
A barrel was hung on the highest mast, and the sailor carried his watch in it. From such a height, the view of the sea was much greater than from the bow of the ship – the sailor could warn the captain in time about the impending danger or that he sees land.