The greater length reduces stylus tracing error, which is a good thing. For pivoted arms, the stylus is aligned perfectly in the groove (i.e., perfectly tangential to the groove the way the cutting stylus cut it) in only two places in its travel across the record. The longer tonearm reduces the amount by which the alignment is off everywhere else. The tradeoff is greater mass and the need for a larger plinth or arm board on which to mount the longer arm.
.
.