Ventajas
The MPI-Inf provides a world-class research environment. The hardware and human resources available are large enough to rarely be an issue. The world class reputation of the institute is backed by world class researchers, and an environment focused on research to its core. The MPI funding schema allows the researcher to works with little to no distraction to their core activity. At MPi-Inf your brain is the only limiting factor to your research productivity.
Desventajas
There is little more going other than research. The location (Saarbruecken) is enjoyable (gardens, shops, 2 hours from Paris by train), but certainly a top destination in Europe. The internal bureaucracy is light, but old-school (e.g. no web interface to declare vacations).