During normal riding you should ride in a dominant position (i.e. more or less in the middle of your lane) allowing for the road surface, parked vehicles and oncoming traffic. Riding too far to the left or right when conditions are clear will get you a rider fault. However, being inflexible when dealing with, particularly, oncoming traffic (in other words not moving to the left allowing more room for the oncoming vehicle) will be viewed more seriously. Likewise being too close to parked cars.