In these days TV series episodes are sometimes rerun within months, sometimes weeks, of their original broadcast and sometimes two or three times in the first year, but there was a time back in the 1960s when the three networks tried to avoid showing reruns at all! Then series produced as many as 39 new episodes a year (compared to maybe 20 to 22 today) so you didn't need to rerun episodes at all until the summer months and often the networks would try to avoid this by running a replacement program instead until the fall. Sometimes this was a cheap original variety show, sometimes they would run a British TV show they had bought (this is how both "The Avengers" and "the Prisoner" first appeared on US TV).
This show was a clever idea of salvaging something from what would ordinarily have been a dead loss. Every year, a number of ideas for new TV shows would get to what was called the "pilot" stage, that is, they would film a sample episode so the powers that be could make a final decision on whether to order a full season of shows. If the pilot was successful, the show would go on the air in the fall, if not that would be the end of it. Some TV exec got the bright idea of putting the failed pilots on as a summer replacement series. Since they were failures, they were of course not of the highest quality, but they undoubtedly felt (and rightly) that it was better to show them than forcing the viewers to watch something again they had already seen. And sometimes it was actually interesting to see familiar stars playing entirely different roles from what you were used to. I particularly remember a pilot Dwayne Hickman made after "Dobie Gillis" went off the air in which he played an elementary school teacher.
