Primary goal if the application is to provide enhanced synchronization of your personal data: the files that you directly or indirecly create yourself and therefore they are most valuable and cannot be obtained from somewhere else. For instance, your MS Office documents, pictures, text files, password manager data or any other files your applications work with. Data replication between multiple computers or with a removable drive allows you to use and modify them when you want and where you want: at home, in the office, in a business trip and so on. Furthermore, you get data backup at no additional effort.
Synchronization of some application data files on our computer can also be a good idea. For example, you may want to add Internet Explorer favorites at work and see them at home and vise-versa. To do so you can synchronize Internet Explorer favorites directories on both computers via USB drive. IE favorites folder is usually located at [drive]:\Documents and Settings\[current_user_name]\Favorites.
Of course, synchronization of data you are not authoring is possible too. Synchronize archive of downloaded software between desktop PC and laptop over local network while at home. And you will be able to install and use that software in flight.