Connectional information is a good use-case for them. I've not seen much commercial advertising on them.
When done properly, but I personally would argue that it’d be useful to start showing this info before the train is already pulling into the platform (TfW the last time I was on them). And I’m not talking about commercial ads, I’m talking about TOC ads. Penalty fares, where to get the best fares, treat staff with respect, were on social media! Etc.
For me, the main use of the PIS should be to inform passengers of the destination and calling points, and not spending most of the time blank and only displaying this info once or twice between each stop at random times (22x looking at you!)