Conversative or moderate setting does really affect the simulation accuracy, also there is some occasion that moderate setting provide completly different waveform than the conversative one due to different time-step control, different numerical integration methods and relative tolerence setting. For example, when simulating digital signals, oscillation (which is come from the failure of the simulation) can occur during transition (This is known as trapezodial oscillation as it is caused by the failure of trapezodial numerical integration methods) if the time step is too large. Usually conversative setting can solve the problem as it used gear2 integration methods. I think Hspice also have such problems, but in Hspice the option setting are usually well defined by the user easily, so it work well. Hope this can help and correct me if I am wrong.