Those and the purpose of the feed. If it was a syndication feed to local stations, it probably had commercials in some breaks and black for other breaks, since, in most cases, the syndicator sells some of the time and the local station sells some. It varies from show to show.
Same goes for network feeds. If it was something like an early feed from networks to stations (like Young and the Restless used to feed in the early morning hours), all of the breaks would be full except for the station break at roughly the half-hour point.
But if it happened to be a true backhaul, for instance, Johnny Carson being fed from LA to NY, there wouldn't be commercials. The band would continue playing with the "more to come" slide on the screen through the entire two-minute break (1 minute for national commercials from NBC New York, 1 minute for local stations.) Again, near half-hour mark, there would be a station break. I think the backhaul still had the band playing throughout, but NBC New York fed out black during the station break.
Same thing with NFL games, but instead of the "more to come" slide, you'd see the teams warming up, the quarterback and head coach talking strategy etc during the two minute break.