Tarmack
Rhetorical Porcupine
Does the network inform about the reasons why your video is denied, in case that happens ?
No it just doesn't happen at all. When you're using Adsense and you "monetize" it, YouTube will often autoflag a video even though nothing is wrong with it asking the user to provide proof of ownership. This process can ultimately result in an appeal or at least delays.
With a network, you click a "claim" check box and monetization begins automatically.
It doesn't protect you from copyright strikes if a content owner has set "Content ID" and decided they want to hit everyone who uploads their stuff, so you still need to be cautious of copyright issues. But it takes a lot of the headache of sending links to TOS agreements or license agreements, etc.