Although theoretical results have been established regarding the utility of pre-emptive scheduling in reducing average job turn-around time, job suspension/restart is not much used in practice at supercomputer centers for parallel job scheduling. A number of questions remain unanswered regarding the practical utility of pre-emptive scheduling. We explore this issue through a simulation-based study, using job logs from a supercomputer center We develop a tunable selective-suspension strategy, and demonstrate its effectiveness. We also present new insights into the effect of pre-emptive scheduling on different job classes and address the impact of suspensions on worst-case slowdown.