feeds
The most common might be news feeds from the field.
There have been quite a lot on lately, due to newsworthy incidents.
The other category seems to be sports feeds.
Often backup channels in case the main feed goes down.
Neither are on a regular schedule, channel, nor satellite.
That's a reason some people have receivers with "blind scan" capability.
On the other hand, with all the birds, and all the transponders, and modest scan speeds, it takes a while to find things.
Some people are happy with that.
You can search the forum for other discussions of feeds, but there is limited discussion due to the fact that publicizing such details is the best way to see them dry up.