The Progress cargo vessels are often given additional tasks of technical or scientific value. Typically performed after they undock from the station.
Many of them participated in the series of Radar-Progress and Plazma-Progress experiments. It takes like 5 days of free flight before the reentry. Progress M-13M has been used as an orbit-to-orbit tug to bring Chibis-M to 500 km orbit. Progress M-04M took part in the Reflection experiment, and so spent 6 weeks in autonomous flight. Etc etc. The tradition goes well into Mir (and may be even Salyut) times.
Are ATV, HTV, Dragon and Cygnus also used as something more than just cargo delivery?