Harbor design & expansion.
At some point I may use fraps and redo this, don't hold your breath.
Plenty of reasons behind expanding your island harbors. An expanded harbor can handle more trade traffic. Adding quay wall spurs - legs lets you build and admire your custom harbor. You can rotate & mold functional useful items such as the Clearance Terminal into your harbor design. You can add eye candy decor such as shipping crates and the quay wall gate. You can also add or attach items such as the Lighthouse, Repair Dock, Harbor Defense Turret, Mobile Harbor Defenses (tech), Submarine base (tech), and the Eco & Tycoon Shipyard. The Fishery can also attach. These items will function just as well independently but many players enjoy customizing their harbor similar to how the computer players harbors appear. Perhaps a trading, defense or military style.
Some island harbors wind up in a cove, where an extended Clearance Terminal would be beneficial for traffic.