I'll try to explain it simple:
Let's say i own the local media firms - all of them (say 4-5) - and one of the competitors use heavily advertising in these firms - i wish i'd be able to ban its products ads from my media - to stop him to get media attention in order to beat him in selling stuff. With no advertising, his corporation will suffer.
I realise this will be awful thing to happen to me. But hey - in reallity this kind of things happen all the time - if you control a media, you can use it to undermine your competition.
So the simple option - ability to ban some companies ads from my media.