Why do I have an exclamation mark in front of my campaign?

Olivier de Lamotte -

You have this issue and wonder where it comes from, what the implications are?

It only comes from the fact that you have several channels for this campaign and that those channels don't have the same start/end dates.

In order to solve this issue, you can modify the dates in order for them to be the same for each channel. 

If you want the dates to vary for each channel, you can just leave it this way, there won't be any implication. Each channel will be displayed at the decided date and all data will be gathered just fine.