The function of a record player is to measure the groove with respect to time.

The more accurate is this measurement the better is the performance of the record player. To measure something accurately, a reference point and its precise location is required. During this measurement the record is rotating and only one thing could locate the precise position of the groove and that is the stylus tip. So it is of paramount importance to keep the stylus/record contact free from any disturbances. The reference point is the axis of rotation. So it is equally important to avoid any 'wobble' in the main bearing.

Internal and external noise and disturbances would also impair the measurement. The stylus is fitted to the tone arm, which in turn is supported by the arm board. So the arm board/main bearing structure requires very careful design to ensure its complete mechanical integrity. The main bearing/platter/motor assembly should also work in such a way that the stylus/record interface is kept free from internal and external disturbances. In short the whole design unfolds from the stylus tip.