I just compared a digital sport servo to a standard ball bearing sport servo. I found that with the standard servo, the control surface did not return to the same position when I let go of the stick (pushed rudder right, let go, then pushed rudder left and let go). There was a difference of about 3 clicks of rudder trim.

I've heard that digital servos 'center' better than standard servos, and I guess this is what they are talking about. The digital servo returns to the same place, at least no difference to the naked eye.

To me, digital servos seem to be more responsive and accurate, and the plane seems quicker to respond.

Well worth the extra $$$ in my beginner's humble opinion.