At our church, we don't usually have a single background slide for all slides. At times, we will change up the backgrounds to match the songs.
When I first started with ProPresenter, I would assign a background to a particular slide so all I had to do was cycle through the slides as the worship progressed. But this turned into a painful exercise because after the service, I would have to remove the backgrounds for the song because we didn't want the backgrounds to be stale always playing the same ones.
So now what I do is I create a new Library folder where I will drag the different types of pictures and moving clips that I want to use for that service and keep that media folder available. This is really useful now that when you click on a background slide, the arrow keys still advance the lyrics.
(In older versions of ProPresenter, when you clicked on a background slide, the arrow keys would then advance the backgrounds instead of the lyrics.)
Now, after a service, I no longer have to delete the backgrounds slides - only the new library folder I created.
And just for fun, sometimes I will change a background while on the same slide for lyrics so that the background matches the words. If done right, it can really help with the visual of what is being sung. If I do this, it is usually at the end of a song where the same words are being sung again.
But remember the golden rule - less is more!