I'm struggling a little with this concept. How does Sky spending subscription money to make promotional adverts about themselves, and upcoming programming, subsidise the subscription viewers pay? Are the programming adverts made by the content sellers who in turn pay Sky to show them?
To let you know about shows that are on and therefore entice you to watch them and serve up even more advertising, just like promos on FTA work. Promotional ads are pretty much the same, like Melody telling us that they have the Sky Perks app, which in theory increasing the value proposition for being a Sky customer, or some guy rambling on about being a Sports customer helps the grassroots of the game. And then there are the times when paid advertising isn't allowed (Sunday mornings, religious holidays) when they need to fill the void with something.