Couldn't I just use a single binding converter and as a parameter pass in the DataContext and from there pick what properties I want to use?
If you pass the whole object instead of the individual properties, then the binding expression will not be re-evaluated when the individual properties change. You will be losing the benefit of the
You might want to be more explicit and take in the minimum extra information (which is just generally good programming practice), or you may want information from more than one source - e.g. Your value might be dependent on a property of the datacontext and the checked state of a checkbox somewhere else in the view.
You can do that, but the binding will not update if the relevant properties change that way. Besides the updates Multibinding is needed for more complex bindings to different controls and data-objects.