A lathe half centre is used

To support the workpiece always

To turn long workpiece

Because it is easy to lubricate the workpiece

To face the workpiece up to the end of the centre hole

Answer is:

To face the workpiece up to the end of the centre hole

Explanation:

Though it is termed as half centre, little less than half is relieved at the tip portion. Used while facing the job without disturbing the setting.