writepss/readpss captures the final steady-state solution, both for shooting and (since recent MMSIM701 ISRs and MMSIM71), harmonic balance. This represents the entire solution - the whole period. Using writefinal/readic only captures the final DC operating point (and reuses it).

Using writefinal/readic means that it still needs to solve from scratch; it's just that the DC for the steady-state may be closer to the final settled value. With writepss/readpss it should be very close to the final solution (it still needs to solve, because the circuit conditions may have changed a little in the meantime, between the run with writepss and the run with readpss).

Does that help?

Regards,

Andrew.