This button does all the same work as the save button, just a little bit more. Sometimes two or more clients are very close to each other, or even in the same building. It is then not possible for the application to correctly distinguish between the locations. The application will select the closest client. This automatically selected client might be wrong. You then need to manually select the right client. This is done by the following button on the main page. 
Sometimes you will visit both clients in the same building. When the first visit is finished, you need to save the information anout the first visit and then create a new visit. This is what this button is for. It asks the same information as the SAVE button and the name of the client of the new visit.