Desserts cannot be separated from the entrees, it's all one credit.
The only difference is the sort of thing described by the above posters, where some CS will allow you to come back in a designated time for ice cream. At TS (which you wouldn't go to on the QS plan) you will have to order your dessert while you're there - you can't go back or go to another restaurant for those. You can, of course, get the dessert to go - but you need to carry it then, and that precludes choosing frozen desserts.