How much of SQL Express is required at user locations?

SQL Express is quite sizable for what I want to do but it appears to have many features that could turn out to be highly desirable.

It makes sense that the entire SQL Express must be installed at the developer's location, but what portion of it is required at the application user's location? All, or some?

Thanks

You still need to install the complete system, by this I mean the standard system. You do not have to install the management tools, but the rest is required.