Audio circuit: single point PLUS ground plane
With a large ground plane the impedance is very much lower than individual tracks and hence any signal current passing through the plane produces a very much smaller associated volt drop. That volt drop might be a lot bigger if your audio circuit has significant gain and ability to drive low value loads.

That volt drop may be quite distorted if you are using push-pull amplifiers. That volt drop (even though you are using a plane) may produce small distorting signals at the sensitive inputs to your amplifier. That can produce feedback and distortion.

On the other hand, if you restrict the higher current flows to their own tracks and star-point all ground returns to one point then it's usually a better choice for audio.


  However, one question arised in my head and I haven't found an answer.
  Is it beneficial to the circuit to make a fill on the PCB, connected
  with ground at the single point?


You seem to be missing the point about star pointing - the point is that you use individual traces/wires to this star point and not a plane that en bloc connects to what is an arbitrary 0 volt reference. The point is to avoid high signal currents mixing with low signal currents and thus creating anomalies.