I have two reasons that work not only within the Star Wars universe, but our own as well:

##Visibility.

When driving any vehicle, it's important for the driver to watch the line of motion to make sure that there aren't obstacles in the path. As the control panel takes up most of the forward display, banking around a turn gives significantly better visibility towards any approaching matter. This can also be seen in the exaggerated banking used to enter the cave on the asteroid.

##Compensation for acceleration dapeners

It should be noted that although the Millennium falcon has artificial gravity, it only partially dampens its own acceleration; this can be seen when R2D2 fixed the Millennium Falcon and it jumped into lightspeed without warning.

When an object accelerates around a curve, the force of the acceleration points inwards toward the center. If you ride in a car and make a turn, you feel a force on the outside of the curve in addition to gravity. This effect would not go away completely in space, due to the effects of artificial acceleration dampening.

The optimal solution for both cases is for the normal vector of the craft's gravity to turn toward the direction of the acceleration, which is what banking is.

I have two reasons that work not only within the Star Wars universe, but our own as well:

Visibility.

When driving any vehicle, it's important for the driver to watch the line of motion to make sure that there aren't obstacles in the path. As the control panel takes up most of the forward display, banking around a turn gives significantly better visibility towards any approaching matter. This can also be seen in the exaggerated banking used to enter the cave on the asteroid.

Compensation for acceleration dapeners

It should be noted that although the Millennium falcon has artificial gravity, it only partially dampens its own acceleration; this can be seen when R2D2 fixed the Millennium Falcon and it jumped into lightspeed without warning.

When an object accelerates around a curve, the force of the acceleration points inwards toward the center. If you ride in a car and make a turn, you feel a force on the outside of the curve in addition to gravity. This effect would not go away completely in space, due to the effects of artificial acceleration dampening.

The optimal solution for both cases is for the normal vector of the craft's gravity to turn toward the direction of the acceleration, which is what banking is.