Is it possible that I might report for service but not sit on a jury?

Yes. The parties involved in a case usually try to settle their differences and avoid the time and expense of a trial. Sometimes a case is settled only minutes before the trial begins. Therefore, even though many trials are scheduled each day, some of them will not actually go to trial, so those cases will not need juries. But your time spent waiting to serve is not wasted; your presence encourages settlement.