I'm not sure how they do it now, but when I served you were not released until your met with your Stake President at home. One can easily see how using the return trip home for a tour/vacation kind of goes against the purpose of mission service. My parents picked up my younger brother at the conclusion of his mission in Sweden. They toured several countries before picking him up, but then visited a couple areas that he served in during his mission (with permission of the MP) just prior to returning home. My dad felt that because he was still set apart as a full time missionary, doing the tourist thing was not following the spirit of missionary service.