SJF cannot be used for practical purposes as one doesn't know BT of process when process is created. If all jobs are available at first, then SJF cannot have convoy effect, but if new process comes and it is non pre-emptive SJF, then there can be convoy effect. We generally consider convoy effect, when we assume that all processes are available. Therefore only, FCFS will definitely have convoy effect. In priority scheduling also convoy effect is possible as longer process may be given higher priority.