As well as your Under 18 and Under 23 Rosters, you will also have access to your regular, everyday squad. Here, you can check on your players' health and morale, as well as negotiate new deals for some and release others.
On top of all of that, a new layer has been added to the depths of each and every player this season. Within FM17, there are the new features of trait development and advanced interaction will all members of your squad. Players are now fully aware of their environment, and this can have a dramatic affect on their career progressions. So if they aren't happy about their contract, playing time or even your facilities, you'll hear about it. Or worse, they'll even go to the Media with it.
Keeping your players both happy and yet hungry can be a balancing act sometimes and a struggle at others; finding the right mix will be critical for not just all parties involved, but also for your team as a whole.