This one actually isn't unique to Ice Cream Sandwich, but it's on by default when you first use your phone. The Android Market now has an option to automatically add shortcuts to your homescreen when you install a new application. You may be fine with that. But if you wan to turn it off, you'll need to go to the Android Market, press the menu button, then choose settings, then uncheck "Auto-add shortcuts." That'll keep shortcuts from being automatically added to your home screen.