I'm afraid this is a practice which has migrated across the Atlantic from the USA. It's meant to keep you watching thier progrrammme and not to channel hop.
In a similar vein the post advert recap, telling you what you've just watched in case you'd forgotten in the last five minutes. Something which until five years ago was rare on UK tv channels.
Doesn't happen on the BBC though.
I hate the caption coming on telling you what's next. Worst perp. is Coronation St. which started this around January. Used to be two mins before the end of the prog, but now it's crept to just after the ad break.
The other one I dislike is the credit squeeze, all channels are guilty of this, which I don't mind on tv progs where they make the credits bigger so they can still be read. But I hate it on feature films when the credits are so small you can't read them to see who the actors were.