Metal seated ball valves are mainly used for heavy duty applications such as:

High temperatures: above 260 ºC the use of soft seats is not recommended.
Abrassive media: even small particles can damage soft seats.
High Velocity in opening/closing cycles: this action can perfectly deform the soft ring and destroy the seat.

Metal seated ball valves for different services (slurries, pulp and liquors, high temperature, abrasive or sticking fluids, control).