WBRC-6 in Birmingham was notorious for their preemptions during the 70's and 80's. Instead of Three's Company and Soap on Tuesday nights from 8-9, viewers were treated to Gunsmoke reruns. (Three's Company and Soap were delayed until the following Monday night after the late news). There was a time when Bewitched was delayed until Saturday evenings at 6 for reruns of the Rifleman. And Charlie's Angels ended up on Sunday afternoons opposite NFL football...again, for reruns of Marshall Dillon. It wasn't until well into the 80's or early 90's that they showed Nightline at all. They also didn't clear ABC's programming from 10-11 a.m. (Central), showing All My Children at that time, and airing a noon newscast and syndicated game shows at 12:30. Not that it mattered a lot to ABC, since WBRC was the dominant station in north-central Alabama at the time.
The three things that crosstown WAPI-13 (now WVTM) preempted once it became a full-time NBC affiliate in 1970 were:
*the second half of NBC's Sunday NFL package; those games went to CBS stations WBMG-42 (now WIAT), WCFT-33 in Tuscaloosa and WHMA-40 (now WJSU) in Anniston. Instead, Channel 13 showed the Bear Bryant Show (Alabama football highlights) and Auburn Football Review with Shug Jordan and later Doug Barfield.
*the first (and maybe second) season of Saturday Night Live, and
*the first season of Late Night with David Letterman.
Also, Channel 13 delayed the Tonight Show from 10:30/10:35 until 11:30/11:35, showing reruns of M*A*S*H at 10:30, and All in the Family, Carol Burnett and Friends, Taxi and the Jeffersons at 11:00. This continued even after Jay Leno took over from Johnny.
WBMG didn't preempt very much, if any CBS programming. It didn't matter much, since their signal was so poor a lot of people didn't even bother watching them, anyways.