(DRY MOTORING) is a common practice, many hangars have an external air supply (no need for APU usage) 20-40psi @ required volume for the motor is mainly a process to perform a leak check after a motor change.
The thrust is not really significant.
It is also a good procedure operationally, to use after a failed (ignititor) start to exaust fuel that can accumulate in the turbine/tailcone prior to selecting the other ignition source to attempt another engine start as a tailcone fire is likely.