The synergies result in a more profitable media production. For example, fox can produce one show and put it on the FOX cable channel and then later put it on FX or FXX. They include clips of shows in their social media accounts to promote the programming that is on that night.
Synergies can definitely have negative effects. For example, FOX News supports views that aren't as environmentally conscious as National Geographic. This might influence the content that Nat. Geo. produces.