What does Setup Assistant do if you sign in with Apple ID?

I would like to know what exactly Setup Assistant does if you sign in with your Apple ID on the first boot of a new Mac (I will be setting up a new Macbook Pro). I ask because in my experience, if you enter your Apple ID on the initial setup of an iPhone, it does various things like transfer your Safari bookmarks from your last iPhone, without telling you it's doing them. I don't want to transfer any information from my old Macbook. I assume that signing in at least sets you up in iTunes and the App Store. Does signing in with your Apple ID in Setup Assistant automatically do other things that it doesn't ask you whether you want to do? Transfer anything or turn on any particular iCloud functionality without asking?

Thanks for your help