Friends/Followers ratio is important, is one of the things that Twitter analyzes in order to let you (or not) follow more accounts.
e.g., your account has 100 friends and 100 followers, the ratio would be 100/100 = 1.
The closer to 0, the better. So, to keep your account healthy, the default setup of your campaigns is to unfollow all those accounts that aren't following you back.
If you want to be more aggressive on the unfollow or not unfollow anyone, you can change the unfollow settings on a campaign level.