AppToService is one of those programs whose abilities will make you say either, "I gotta get me that!" or "Huh?" I admit to being slightly in the "Huh?" camp, but I do see the use of the program on a server or a network. Any application which needs to be "always on"-- whether a user is logged in to the computer or not--can benefit from this treatment.
What AppToService does is, simply, turn any Windows application into a Windows service. This has several implications. The app can then run when no user is logged on. It can run as a user other than the logged-in user. It can start when Windows starts. The usefulness of this is mostly for applications which need to be always on--a database, a mail server, or a security tool, for example. AppToService also can be used to allow a program which needs one particular user's privileges to be running no matter who is logged in.
As you can see, AppToService is of greatest use in a corporate or other multi-user environment. While there may be specialist uses, the average home user will not need this program--but network administrators might want to take a good look at it.