well aside from all the benefits harmalas add to the equation...
changa is much easier to smoke, tastes better, smells better, less likely for pipe melt-through, easier to handle and work with (weigh out, load, whatever), less sketchy looking, and you don't have to worry about burning it. Not to mention you can add in a bunch of your favorite herbs, stirring in whatever properties they bring to the table
i'd always take changa in a bong over just freebase alone