What are the advantages and disadvantages of having landing gear doors?
Benefits of gear doors


With gear doors, there are fewer constraints on the retracted gear position. This is especially important in larger aircraft with larger and more complex landing gear. It doesn't need to be flush with fuselage or streamlined (737 also uses hubcaps).
The gear doors provide a good aerodynamic surface
Opening to gear bay can be larger and easier to access


Drawbacks of gear doors


Extra weight for the door and the mechanisms
Extra complexity of opening another door (possibility for things to go wrong)